mballoc.c

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/*
 * Copyright (c) 2003-2006, Cluster File Systems, Inc, [email protected]
 * Written by Alex Tomas <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public Licens
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-
 */


/*
 * mballoc.c contains the multiblocks allocation routines
 */

#include "ext4_jbd2.h"
#include "mballoc.h"
#include <linux/debugfs.h>
#include <linux/log2.h>
#include <linux/slab.h>
#include <trace/events/ext4.h>

/*
 * MUSTDO:
 *   - test ext4_ext_search_left() and ext4_ext_search_right()
 *   - search for metadata in few groups
 *
 * TODO v4:
 *   - normalization should take into account whether file is still open
 *   - discard preallocations if no free space left (policy?)
 *   - don't normalize tails
 *   - quota
 *   - reservation for superuser
 *
 * TODO v3:
 *   - bitmap read-ahead (proposed by Oleg Drokin aka green)
 *   - track min/max extents in each group for better group selection
 *   - mb_mark_used() may allocate chunk right after splitting buddy
 *   - tree of groups sorted by number of free blocks
 *   - error handling
 */

/*
 * The allocation request involve request for multiple number of blocks
 * near to the goal(block) value specified.
 *
 * During initialization phase of the allocator we decide to use the
 * group preallocation or inode preallocation depending on the size of
 * the file. The size of the file could be the resulting file size we
 * would have after allocation, or the current file size, which ever
 * is larger. If the size is less than sbi->s_mb_stream_request we
 * select to use the group preallocation. The default value of
 * s_mb_stream_request is 16 blocks. This can also be tuned via
 * /sys/fs/ext4/<partition>/mb_stream_req. The value is represented in
 * terms of number of blocks.
 *
 * The main motivation for having small file use group preallocation is to
 * ensure that we have small files closer together on the disk.
 *
 * First stage the allocator looks at the inode prealloc list,
 * ext4_inode_info->i_prealloc_list, which contains list of prealloc
 * spaces for this particular inode. The inode prealloc space is
 * represented as:
 *
 * pa_lstart -> the logical start block for this prealloc space
 * pa_pstart -> the physical start block for this prealloc space
 * pa_len    -> length for this prealloc space (in clusters)
 * pa_free   ->  free space available in this prealloc space (in clusters)
 *
 * The inode preallocation space is used looking at the _logical_ start
 * block. If only the logical file block falls within the range of prealloc
 * space we will consume the particular prealloc space. This makes sure that
 * we have contiguous physical blocks representing the file blocks
 *
 * The important thing to be noted in case of inode prealloc space is that
 * we don't modify the values associated to inode prealloc space except
 * pa_free.
 *
 * If we are not able to find blocks in the inode prealloc space and if we
 * have the group allocation flag set then we look at the locality group
 * prealloc space. These are per CPU prealloc list represented as
 *
 * ext4_sb_info.s_locality_groups[smp_processor_id()]
 *
 * The reason for having a per cpu locality group is to reduce the contention
 * between CPUs. It is possible to get scheduled at this point.
 *
 * The locality group prealloc space is used looking at whether we have
 * enough free space (pa_free) within the prealloc space.
 *
 * If we can't allocate blocks via inode prealloc or/and locality group
 * prealloc then we look at the buddy cache. The buddy cache is represented
 * by ext4_sb_info.s_buddy_cache (struct inode) whose file offset gets
 * mapped to the buddy and bitmap information regarding different
 * groups. The buddy information is attached to buddy cache inode so that
 * we can access them through the page cache. The information regarding
 * each group is loaded via ext4_mb_load_buddy.  The information involve
 * block bitmap and buddy information. The information are stored in the
 * inode as:
 *
 *  {                        page                        }
 *  [ group 0 bitmap][ group 0 buddy] [group 1][ group 1]...
 *
 *
 * one block each for bitmap and buddy information.  So for each group we
 * take up 2 blocks. A page can contain blocks_per_page (PAGE_CACHE_SIZE /
 * blocksize) blocks.  So it can have information regarding groups_per_page
 * which is blocks_per_page/2
 *
 * The buddy cache inode is not stored on disk. The inode is thrown
 * away when the filesystem is unmounted.
 *
 * We look for count number of blocks in the buddy cache. If we were able
 * to locate that many free blocks we return with additional information
 * regarding rest of the contiguous physical block available
 *
 * Before allocating blocks via buddy cache we normalize the request
 * blocks. This ensure we ask for more blocks that we needed. The extra
 * blocks that we get after allocation is added to the respective prealloc
 * list. In case of inode preallocation we follow a list of heuristics
 * based on file size. This can be found in ext4_mb_normalize_request. If
 * we are doing a group prealloc we try to normalize the request to
 * sbi->s_mb_group_prealloc.  The default value of s_mb_group_prealloc is
 * dependent on the cluster size; for non-bigalloc file systems, it is
 * 512 blocks. This can be tuned via
 * /sys/fs/ext4/<partition>/mb_group_prealloc. The value is represented in
 * terms of number of blocks. If we have mounted the file system with -O
 * stripe=<value> option the group prealloc request is normalized to the
 * the smallest multiple of the stripe value (sbi->s_stripe) which is
 * greater than the default mb_group_prealloc.
 *
 * The regular allocator (using the buddy cache) supports a few tunables.
 *
 * /sys/fs/ext4/<partition>/mb_min_to_scan
 * /sys/fs/ext4/<partition>/mb_max_to_scan
 * /sys/fs/ext4/<partition>/mb_order2_req
 *
 * The regular allocator uses buddy scan only if the request len is power of
 * 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
 * value of s_mb_order2_reqs can be tuned via
 * /sys/fs/ext4/<partition>/mb_order2_req.  If the request len is equal to
 * stripe size (sbi->s_stripe), we try to search for contiguous block in
 * stripe size. This should result in better allocation on RAID setups. If
 * not, we search in the specific group using bitmap for best extents. The
 * tunable min_to_scan and max_to_scan control the behaviour here.
 * min_to_scan indicate how long the mballoc __must__ look for a best
 * extent and max_to_scan indicates how long the mballoc __can__ look for a
 * best extent in the found extents. Searching for the blocks starts with
 * the group specified as the goal value in allocation context via
 * ac_g_ex. Each group is first checked based on the criteria whether it
 * can be used for allocation. ext4_mb_good_group explains how the groups are
 * checked.
 *
 * Both the prealloc space are getting populated as above. So for the first
 * request we will hit the buddy cache which will result in this prealloc
 * space getting filled. The prealloc space is then later used for the
 * subsequent request.
 */

/*
 * mballoc operates on the following data:
 *  - on-disk bitmap
 *  - in-core buddy (actually includes buddy and bitmap)
 *  - preallocation descriptors (PAs)
 *
 * there are two types of preallocations:
 *  - inode
 *    assiged to specific inode and can be used for this inode only.
 *    it describes part of inode's space preallocated to specific
 *    physical blocks. any block from that preallocated can be used
 *    independent. the descriptor just tracks number of blocks left
 *    unused. so, before taking some block from descriptor, one must
 *    make sure corresponded logical block isn't allocated yet. this
 *    also means that freeing any block within descriptor's range
 *    must discard all preallocated blocks.
 *  - locality group
 *    assigned to specific locality group which does not translate to
 *    permanent set of inodes: inode can join and leave group. space
 *    from this type of preallocation can be used for any inode. thus
 *    it's consumed from the beginning to the end.
 *
 * relation between them can be expressed as:
 *    in-core buddy = on-disk bitmap + preallocation descriptors
 *
 * this mean blocks mballoc considers used are:
 *  - allocated blocks (persistent)
 *  - preallocated blocks (non-persistent)
 *
 * consistency in mballoc world means that at any time a block is either
 * free or used in ALL structures. notice: "any time" should not be read
 * literally -- time is discrete and delimited by locks.
 *
 *  to keep it simple, we don't use block numbers, instead we count number of
 *  blocks: how many blocks marked used/free in on-disk bitmap, buddy and PA.
 *
 * all operations can be expressed as:
 *  - init buddy:           buddy = on-disk + PAs
 *  - new PA:               buddy += N; PA = N
 *  - use inode PA:         on-disk += N; PA -= N
 *  - discard inode PA          buddy -= on-disk - PA; PA = 0
 *  - use locality group PA     on-disk += N; PA -= N
 *  - discard locality group PA     buddy -= PA; PA = 0
 *  note: 'buddy -= on-disk - PA' is used to show that on-disk bitmap
 *        is used in real operation because we can't know actual used
 *        bits from PA, only from on-disk bitmap
 *
 * if we follow this strict logic, then all operations above should be atomic.
 * given some of them can block, we'd have to use something like semaphores
 * killing performance on high-end SMP hardware. let's try to relax it using
 * the following knowledge:
 *  1) if buddy is referenced, it's already initialized
 *  2) while block is used in buddy and the buddy is referenced,
 *     nobody can re-allocate that block
 *  3) we work on bitmaps and '+' actually means 'set bits'. if on-disk has
 *     bit set and PA claims same block, it's OK. IOW, one can set bit in
 *     on-disk bitmap if buddy has same bit set or/and PA covers corresponded
 *     block
 *
 * so, now we're building a concurrency table:
 *  - init buddy vs.
 *    - new PA
 *      blocks for PA are allocated in the buddy, buddy must be referenced
 *      until PA is linked to allocation group to avoid concurrent buddy init
 *    - use inode PA
 *      we need to make sure that either on-disk bitmap or PA has uptodate data
 *      given (3) we care that PA-=N operation doesn't interfere with init
 *    - discard inode PA
 *      the simplest way would be to have buddy initialized by the discard
 *    - use locality group PA
 *      again PA-=N must be serialized with init
 *    - discard locality group PA
 *      the simplest way would be to have buddy initialized by the discard
 *  - new PA vs.
 *    - use inode PA
 *      i_data_sem serializes them
 *    - discard inode PA
 *      discard process must wait until PA isn't used by another process
 *    - use locality group PA
 *      some mutex should serialize them
 *    - discard locality group PA
 *      discard process must wait until PA isn't used by another process
 *  - use inode PA
 *    - use inode PA
 *      i_data_sem or another mutex should serializes them
 *    - discard inode PA
 *      discard process must wait until PA isn't used by another process
 *    - use locality group PA
 *      nothing wrong here -- they're different PAs covering different blocks
 *    - discard locality group PA
 *      discard process must wait until PA isn't used by another process
 *
 * now we're ready to make few consequences:
 *  - PA is referenced and while it is no discard is possible
 *  - PA is referenced until block isn't marked in on-disk bitmap
 *  - PA changes only after on-disk bitmap
 *  - discard must not compete with init. either init is done before
 *    any discard or they're serialized somehow
 *  - buddy init as sum of on-disk bitmap and PAs is done atomically
 *
 * a special case when we've used PA to emptiness. no need to modify buddy
 * in this case, but we should care about concurrent init
 *
 */

 /*
 * Logic in few words:
 *
 *  - allocation:
 *    load group
 *    find blocks
 *    mark bits in on-disk bitmap
 *    release group
 *
 *  - use preallocation:
 *    find proper PA (per-inode or group)
 *    load group
 *    mark bits in on-disk bitmap
 *    release group
 *    release PA
 *
 *  - free:
 *    load group
 *    mark bits in on-disk bitmap
 *    release group
 *
 *  - discard preallocations in group:
 *    mark PAs deleted
 *    move them onto local list
 *    load on-disk bitmap
 *    load group
 *    remove PA from object (inode or locality group)
 *    mark free blocks in-core
 *
 *  - discard inode's preallocations:
 */

/*
 * Locking rules
 *
 * Locks:
 *  - bitlock on a group    (group)
 *  - object (inode/locality)   (object)
 *  - per-pa lock       (pa)
 *
 * Paths:
 *  - new pa
 *    object
 *    group
 *
 *  - find and use pa:
 *    pa
 *
 *  - release consumed pa:
 *    pa
 *    group
 *    object
 *
 *  - generate in-core bitmap:
 *    group
 *        pa
 *
 *  - discard all for given object (inode, locality group):
 *    object
 *        pa
 *    group
 *
 *  - discard all for given group:
 *    group
 *        pa
 *    group
 *        object
 *
 */
static struct kmem_cache *ext4_pspace_cachep;
static struct kmem_cache *ext4_ac_cachep;
static struct kmem_cache *ext4_free_data_cachep;

/* We create slab caches for groupinfo data structures based on the
 * superblock block size.  There will be one per mounted filesystem for
 * each unique s_blocksize_bits */
#define NR_GRPINFO_CACHES 8
static struct kmem_cache *ext4_groupinfo_caches[NR_GRPINFO_CACHES];

static const char *ext4_groupinfo_slab_names[NR_GRPINFO_CACHES] = {
    "ext4_groupinfo_1k", "ext4_groupinfo_2k", "ext4_groupinfo_4k",
    "ext4_groupinfo_8k", "ext4_groupinfo_16k", "ext4_groupinfo_32k",
    "ext4_groupinfo_64k", "ext4_groupinfo_128k"
};

static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
                    ext4_group_t group);
static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
                        ext4_group_t group);
static void ext4_free_data_callback(struct super_block *sb,
                struct ext4_journal_cb_entry *jce, int rc);

static inline void *mb_correct_addr_and_bit(int *bit, void *addr)
{
#if BITS_PER_LONG == 64
    *bit += ((unsigned long) addr & 7UL) << 3;
    addr = (void *) ((unsigned long) addr & ~7UL);
#elif BITS_PER_LONG == 32
    *bit += ((unsigned long) addr & 3UL) << 3;
    addr = (void *) ((unsigned long) addr & ~3UL);
#else
#error "how many bits you are?!"
#endif
    return addr;
}

static inline int mb_test_bit(int bit, void *addr)
{
    /*
     * ext4_test_bit on architecture like powerpc
     * needs unsigned long aligned address
     */
    addr = mb_correct_addr_and_bit(&bit, addr);
    return ext4_test_bit(bit, addr);
}

static inline void mb_set_bit(int bit, void *addr)
{
    addr = mb_correct_addr_and_bit(&bit, addr);
    ext4_set_bit(bit, addr);
}

static inline void mb_clear_bit(int bit, void *addr)
{
    addr = mb_correct_addr_and_bit(&bit, addr);
    ext4_clear_bit(bit, addr);
}

static inline int mb_find_next_zero_bit(void *addr, int max, int start)
{
    int fix = 0, ret, tmpmax;
    addr = mb_correct_addr_and_bit(&fix, addr);
    tmpmax = max + fix;
    start += fix;

    ret = ext4_find_next_zero_bit(addr, tmpmax, start) - fix;
    if (ret > max)
        return max;
    return ret;
}

static inline int mb_find_next_bit(void *addr, int max, int start)
{
    int fix = 0, ret, tmpmax;
    addr = mb_correct_addr_and_bit(&fix, addr);
    tmpmax = max + fix;
    start += fix;

    ret = ext4_find_next_bit(addr, tmpmax, start) - fix;
    if (ret > max)
        return max;
    return ret;
}

static void *mb_find_buddy(struct ext4_buddy *e4b, int order, int *max)
{
    char *bb;

    BUG_ON(e4b->bd_bitmap == e4b->bd_buddy);
    BUG_ON(max == NULL);

    if (order > e4b->bd_blkbits + 1) {
        *max = 0;
        return NULL;
    }

    /* at order 0 we see each particular block */
    if (order == 0) {
        *max = 1 << (e4b->bd_blkbits + 3);
        return e4b->bd_bitmap;
    }

    bb = e4b->bd_buddy + EXT4_SB(e4b->bd_sb)->s_mb_offsets[order];
    *max = EXT4_SB(e4b->bd_sb)->s_mb_maxs[order];

    return bb;
}

#ifdef DOUBLE_CHECK
static void mb_free_blocks_double(struct inode *inode, struct ext4_buddy *e4b,
               int first, int count)
{
    int i;
    struct super_block *sb = e4b->bd_sb;

    if (unlikely(e4b->bd_info->bb_bitmap == NULL))
        return;
    assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
    for (i = 0; i < count; i++) {
        if (!mb_test_bit(first + i, e4b->bd_info->bb_bitmap)) {
            ext4_fsblk_t blocknr;

            blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
            blocknr += EXT4_C2B(EXT4_SB(sb), first + i);
            ext4_grp_locked_error(sb, e4b->bd_group,
                          inode ? inode->i_ino : 0,
                          blocknr,
                          "freeing block already freed "
                          "(bit %u)",
                          first + i);
        }
        mb_clear_bit(first + i, e4b->bd_info->bb_bitmap);
    }
}

static void mb_mark_used_double(struct ext4_buddy *e4b, int first, int count)
{
    int i;

    if (unlikely(e4b->bd_info->bb_bitmap == NULL))
        return;
    assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
    for (i = 0; i < count; i++) {
        BUG_ON(mb_test_bit(first + i, e4b->bd_info->bb_bitmap));
        mb_set_bit(first + i, e4b->bd_info->bb_bitmap);
    }
}

static void mb_cmp_bitmaps(struct ext4_buddy *e4b, void *bitmap)
{
    if (memcmp(e4b->bd_info->bb_bitmap, bitmap, e4b->bd_sb->s_blocksize)) {
        unsigned char *b1, *b2;
        int i;
        b1 = (unsigned char *) e4b->bd_info->bb_bitmap;
        b2 = (unsigned char *) bitmap;
        for (i = 0; i < e4b->bd_sb->s_blocksize; i++) {
            if (b1[i] != b2[i]) {
                ext4_msg(e4b->bd_sb, KERN_ERR,
                     "corruption in group %u "
                     "at byte %u(%u): %x in copy != %x "
                     "on disk/prealloc",
                     e4b->bd_group, i, i * 8, b1[i], b2[i]);
                BUG();
            }
        }
    }
}

#else
static inline void mb_free_blocks_double(struct inode *inode,
                struct ext4_buddy *e4b, int first, int count)
{
    return;
}
static inline void mb_mark_used_double(struct ext4_buddy *e4b,
                        int first, int count)
{
    return;
}
static inline void mb_cmp_bitmaps(struct ext4_buddy *e4b, void *bitmap)
{
    return;
}
#endif

#ifdef AGGRESSIVE_CHECK

#define MB_CHECK_ASSERT(assert)                     \
do {                                    \
    if (!(assert)) {                        \
        printk(KERN_EMERG                   \
            "Assertion failure in %s() at %s:%d: \"%s\"\n", \
            function, file, line, # assert);        \
        BUG();                          \
    }                               \
} while (0)

static int __mb_check_buddy(struct ext4_buddy *e4b, char *file,
                const char *function, int line)
{
    struct super_block *sb = e4b->bd_sb;
    int order = e4b->bd_blkbits + 1;
    int max;
    int max2;
    int i;
    int j;
    int k;
    int count;
    struct ext4_group_info *grp;
    int fragments = 0;
    int fstart;
    struct list_head *cur;
    void *buddy;
    void *buddy2;

    {
        static int mb_check_counter;
        if (mb_check_counter++ % 100 != 0)
            return 0;
    }

    while (order > 1) {
        buddy = mb_find_buddy(e4b, order, &max);
        MB_CHECK_ASSERT(buddy);
        buddy2 = mb_find_buddy(e4b, order - 1, &max2);
        MB_CHECK_ASSERT(buddy2);
        MB_CHECK_ASSERT(buddy != buddy2);
        MB_CHECK_ASSERT(max * 2 == max2);

        count = 0;
        for (i = 0; i < max; i++) {

            if (mb_test_bit(i, buddy)) {
                /* only single bit in buddy2 may be 1 */
                if (!mb_test_bit(i << 1, buddy2)) {
                    MB_CHECK_ASSERT(
                        mb_test_bit((i<<1)+1, buddy2));
                } else if (!mb_test_bit((i << 1) + 1, buddy2)) {
                    MB_CHECK_ASSERT(
                        mb_test_bit(i << 1, buddy2));
                }
                continue;
            }

            /* both bits in buddy2 must be 1 */
            MB_CHECK_ASSERT(mb_test_bit(i << 1, buddy2));
            MB_CHECK_ASSERT(mb_test_bit((i << 1) + 1, buddy2));

            for (j = 0; j < (1 << order); j++) {
                k = (i * (1 << order)) + j;
                MB_CHECK_ASSERT(
                    !mb_test_bit(k, e4b->bd_bitmap));
            }
            count++;
        }
        MB_CHECK_ASSERT(e4b->bd_info->bb_counters[order] == count);
        order--;
    }

    fstart = -1;
    buddy = mb_find_buddy(e4b, 0, &max);
    for (i = 0; i < max; i++) {
        if (!mb_test_bit(i, buddy)) {
            MB_CHECK_ASSERT(i >= e4b->bd_info->bb_first_free);
            if (fstart == -1) {
                fragments++;
                fstart = i;
            }
            continue;
        }
        fstart = -1;
        /* check used bits only */
        for (j = 0; j < e4b->bd_blkbits + 1; j++) {
            buddy2 = mb_find_buddy(e4b, j, &max2);
            k = i >> j;
            MB_CHECK_ASSERT(k < max2);
            MB_CHECK_ASSERT(mb_test_bit(k, buddy2));
        }
    }
    MB_CHECK_ASSERT(!EXT4_MB_GRP_NEED_INIT(e4b->bd_info));
    MB_CHECK_ASSERT(e4b->bd_info->bb_fragments == fragments);

    grp = ext4_get_group_info(sb, e4b->bd_group);
    list_for_each(cur, &grp->bb_prealloc_list) {
        ext4_group_t groupnr;
        struct ext4_prealloc_space *pa;
        pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
        ext4_get_group_no_and_offset(sb, pa->pa_pstart, &groupnr, &k);
        MB_CHECK_ASSERT(groupnr == e4b->bd_group);
        for (i = 0; i < pa->pa_len; i++)
            MB_CHECK_ASSERT(mb_test_bit(k + i, buddy));
    }
    return 0;
}
#undef MB_CHECK_ASSERT
#define mb_check_buddy(e4b) __mb_check_buddy(e4b,   \
                    __FILE__, __func__, __LINE__)
#else
#define mb_check_buddy(e4b)
#endif

/*
 * Divide blocks started from @first with length @len into
 * smaller chunks with power of 2 blocks.
 * Clear the bits in bitmap which the blocks of the chunk(s) covered,
 * then increase bb_counters[] for corresponded chunk size.
 */
static void ext4_mb_mark_free_simple(struct super_block *sb,
                void *buddy, ext4_grpblk_t first, ext4_grpblk_t len,
                    struct ext4_group_info *grp)
{
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    ext4_grpblk_t min;
    ext4_grpblk_t max;
    ext4_grpblk_t chunk;
    unsigned short border;

    BUG_ON(len > EXT4_CLUSTERS_PER_GROUP(sb));

    border = 2 << sb->s_blocksize_bits;

    while (len > 0) {
        /* find how many blocks can be covered since this position */
        max = ffs(first | border) - 1;

        /* find how many blocks of power 2 we need to mark */
        min = fls(len) - 1;

        if (max < min)
            min = max;
        chunk = 1 << min;

        /* mark multiblock chunks only */
        grp->bb_counters[min]++;
        if (min > 0)
            mb_clear_bit(first >> min,
                     buddy + sbi->s_mb_offsets[min]);

        len -= chunk;
        first += chunk;
    }
}

/*
 * Cache the order of the largest free extent we have available in this block
 * group.
 */
static void
mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
{
    int i;
    int bits;

    grp->bb_largest_free_order = -1; /* uninit */

    bits = sb->s_blocksize_bits + 1;
    for (i = bits; i >= 0; i--) {
        if (grp->bb_counters[i] > 0) {
            grp->bb_largest_free_order = i;
            break;
        }
    }
}

static noinline_for_stack
void ext4_mb_generate_buddy(struct super_block *sb,
                void *buddy, void *bitmap, ext4_group_t group)
{
    struct ext4_group_info *grp = ext4_get_group_info(sb, group);
    ext4_grpblk_t max = EXT4_CLUSTERS_PER_GROUP(sb);
    ext4_grpblk_t i = 0;
    ext4_grpblk_t first;
    ext4_grpblk_t len;
    unsigned free = 0;
    unsigned fragments = 0;
    unsigned long long period = get_cycles();

    /* initialize buddy from bitmap which is aggregation
     * of on-disk bitmap and preallocations */
    i = mb_find_next_zero_bit(bitmap, max, 0);
    grp->bb_first_free = i;
    while (i < max) {
        fragments++;
        first = i;
        i = mb_find_next_bit(bitmap, max, i);
        len = i - first;
        free += len;
        if (len > 1)
            ext4_mb_mark_free_simple(sb, buddy, first, len, grp);
        else
            grp->bb_counters[0]++;
        if (i < max)
            i = mb_find_next_zero_bit(bitmap, max, i);
    }
    grp->bb_fragments = fragments;

    if (free != grp->bb_free) {
        ext4_grp_locked_error(sb, group, 0, 0,
                      "%u clusters in bitmap, %u in gd",
                      free, grp->bb_free);
        /*
         * If we intent to continue, we consider group descritor
         * corrupt and update bb_free using bitmap value
         */
        grp->bb_free = free;
    }
    mb_set_largest_free_order(sb, grp);

    clear_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &(grp->bb_state));

    period = get_cycles() - period;
    spin_lock(&EXT4_SB(sb)->s_bal_lock);
    EXT4_SB(sb)->s_mb_buddies_generated++;
    EXT4_SB(sb)->s_mb_generation_time += period;
    spin_unlock(&EXT4_SB(sb)->s_bal_lock);
}

/* The buddy information is attached the buddy cache inode
 * for convenience. The information regarding each group
 * is loaded via ext4_mb_load_buddy. The information involve
 * block bitmap and buddy information. The information are
 * stored in the inode as
 *
 * {                        page                        }
 * [ group 0 bitmap][ group 0 buddy] [group 1][ group 1]...
 *
 *
 * one block each for bitmap and buddy information.
 * So for each group we take up 2 blocks. A page can
 * contain blocks_per_page (PAGE_CACHE_SIZE / blocksize)  blocks.
 * So it can have information regarding groups_per_page which
 * is blocks_per_page/2
 *
 * Locking note:  This routine takes the block group lock of all groups
 * for this page; do not hold this lock when calling this routine!
 */

static int ext4_mb_init_cache(struct page *page, char *incore)
{
    ext4_group_t ngroups;
    int blocksize;
    int blocks_per_page;
    int groups_per_page;
    int err = 0;
    int i;
    ext4_group_t first_group, group;
    int first_block;
    struct super_block *sb;
    struct buffer_head *bhs;
    struct buffer_head **bh = NULL;
    struct inode *inode;
    char *data;
    char *bitmap;
    struct ext4_group_info *grinfo;

    mb_debug(1, "init page %lu\n", page->index);

    inode = page->mapping->host;
    sb = inode->i_sb;
    ngroups = ext4_get_groups_count(sb);
    blocksize = 1 << inode->i_blkbits;
    blocks_per_page = PAGE_CACHE_SIZE / blocksize;

    groups_per_page = blocks_per_page >> 1;
    if (groups_per_page == 0)
        groups_per_page = 1;

    /* allocate buffer_heads to read bitmaps */
    if (groups_per_page > 1) {
        i = sizeof(struct buffer_head *) * groups_per_page;
        bh = kzalloc(i, GFP_NOFS);
        if (bh == NULL) {
            err = -ENOMEM;
            goto out;
        }
    } else
        bh = &bhs;

    first_group = page->index * blocks_per_page / 2;

    /* read all groups the page covers into the cache */
    for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
        if (group >= ngroups)
            break;

        grinfo = ext4_get_group_info(sb, group);
        /*
         * If page is uptodate then we came here after online resize
         * which added some new uninitialized group info structs, so
         * we must skip all initialized uptodate buddies on the page,
         * which may be currently in use by an allocating task.
         */
        if (PageUptodate(page) && !EXT4_MB_GRP_NEED_INIT(grinfo)) {
            bh[i] = NULL;
            continue;
        }
        if (!(bh[i] = ext4_read_block_bitmap_nowait(sb, group))) {
            err = -ENOMEM;
            goto out;
        }
        mb_debug(1, "read bitmap for group %u\n", group);
    }

    /* wait for I/O completion */
    for (i = 0, group = first_group; i < groups_per_page; i++, group++) {
        if (bh[i] && ext4_wait_block_bitmap(sb, group, bh[i])) {
            err = -EIO;
            goto out;
        }
    }

    first_block = page->index * blocks_per_page;
    for (i = 0; i < blocks_per_page; i++) {
        int group;

        group = (first_block + i) >> 1;
        if (group >= ngroups)
            break;

        if (!bh[group - first_group])
            /* skip initialized uptodate buddy */
            continue;

        /*
         * data carry information regarding this
         * particular group in the format specified
         * above
         *
         */
        data = page_address(page) + (i * blocksize);
        bitmap = bh[group - first_group]->b_data;

        /*
         * We place the buddy block and bitmap block
         * close together
         */
        if ((first_block + i) & 1) {
            /* this is block of buddy */
            BUG_ON(incore == NULL);
            mb_debug(1, "put buddy for group %u in page %lu/%x\n",
                group, page->index, i * blocksize);
            trace_ext4_mb_buddy_bitmap_load(sb, group);
            grinfo = ext4_get_group_info(sb, group);
            grinfo->bb_fragments = 0;
            memset(grinfo->bb_counters, 0,
                   sizeof(*grinfo->bb_counters) *
                (sb->s_blocksize_bits+2));
            /*
             * incore got set to the group block bitmap below
             */
            ext4_lock_group(sb, group);
            /* init the buddy */
            memset(data, 0xff, blocksize);
            ext4_mb_generate_buddy(sb, data, incore, group);
            ext4_unlock_group(sb, group);
            incore = NULL;
        } else {
            /* this is block of bitmap */
            BUG_ON(incore != NULL);
            mb_debug(1, "put bitmap for group %u in page %lu/%x\n",
                group, page->index, i * blocksize);
            trace_ext4_mb_bitmap_load(sb, group);

            /* see comments in ext4_mb_put_pa() */
            ext4_lock_group(sb, group);
            memcpy(data, bitmap, blocksize);

            /* mark all preallocated blks used in in-core bitmap */
            ext4_mb_generate_from_pa(sb, data, group);
            ext4_mb_generate_from_freelist(sb, data, group);
            ext4_unlock_group(sb, group);

            /* set incore so that the buddy information can be
             * generated using this
             */
            incore = data;
        }
    }
    SetPageUptodate(page);

out:
    if (bh) {
        for (i = 0; i < groups_per_page; i++)
            brelse(bh[i]);
        if (bh != &bhs)
            kfree(bh);
    }
    return err;
}

/*
 * Lock the buddy and bitmap pages. This make sure other parallel init_group
 * on the same buddy page doesn't happen whild holding the buddy page lock.
 * Return locked buddy and bitmap pages on e4b struct. If buddy and bitmap
 * are on the same page e4b->bd_buddy_page is NULL and return value is 0.
 */
static int ext4_mb_get_buddy_page_lock(struct super_block *sb,
        ext4_group_t group, struct ext4_buddy *e4b)
{
    struct inode *inode = EXT4_SB(sb)->s_buddy_cache;
    int block, pnum, poff;
    int blocks_per_page;
    struct page *page;

    e4b->bd_buddy_page = NULL;
    e4b->bd_bitmap_page = NULL;

    blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;
    /*
     * the buddy cache inode stores the block bitmap
     * and buddy information in consecutive blocks.
     * So for each group we need two blocks.
     */
    block = group * 2;
    pnum = block / blocks_per_page;
    poff = block % blocks_per_page;
    page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);
    if (!page)
        return -EIO;
    BUG_ON(page->mapping != inode->i_mapping);
    e4b->bd_bitmap_page = page;
    e4b->bd_bitmap = page_address(page) + (poff * sb->s_blocksize);

    if (blocks_per_page >= 2) {
        /* buddy and bitmap are on the same page */
        return 0;
    }

    block++;
    pnum = block / blocks_per_page;
    page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);
    if (!page)
        return -EIO;
    BUG_ON(page->mapping != inode->i_mapping);
    e4b->bd_buddy_page = page;
    return 0;
}

static void ext4_mb_put_buddy_page_lock(struct ext4_buddy *e4b)
{
    if (e4b->bd_bitmap_page) {
        unlock_page(e4b->bd_bitmap_page);
        page_cache_release(e4b->bd_bitmap_page);
    }
    if (e4b->bd_buddy_page) {
        unlock_page(e4b->bd_buddy_page);
        page_cache_release(e4b->bd_buddy_page);
    }
}

/*
 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the
 * block group lock of all groups for this page; do not hold the BG lock when
 * calling this routine!
 */
static noinline_for_stack
int ext4_mb_init_group(struct super_block *sb, ext4_group_t group)
{

    struct ext4_group_info *this_grp;
    struct ext4_buddy e4b;
    struct page *page;
    int ret = 0;

    mb_debug(1, "init group %u\n", group);
    this_grp = ext4_get_group_info(sb, group);
    /*
     * This ensures that we don't reinit the buddy cache
     * page which map to the group from which we are already
     * allocating. If we are looking at the buddy cache we would
     * have taken a reference using ext4_mb_load_buddy and that
     * would have pinned buddy page to page cache.
     */
    ret = ext4_mb_get_buddy_page_lock(sb, group, &e4b);
    if (ret || !EXT4_MB_GRP_NEED_INIT(this_grp)) {
        /*
         * somebody initialized the group
         * return without doing anything
         */
        goto err;
    }

    page = e4b.bd_bitmap_page;
    ret = ext4_mb_init_cache(page, NULL);
    if (ret)
        goto err;
    if (!PageUptodate(page)) {
        ret = -EIO;
        goto err;
    }
    mark_page_accessed(page);

    if (e4b.bd_buddy_page == NULL) {
        /*
         * If both the bitmap and buddy are in
         * the same page we don't need to force
         * init the buddy
         */
        ret = 0;
        goto err;
    }
    /* init buddy cache */
    page = e4b.bd_buddy_page;
    ret = ext4_mb_init_cache(page, e4b.bd_bitmap);
    if (ret)
        goto err;
    if (!PageUptodate(page)) {
        ret = -EIO;
        goto err;
    }
    mark_page_accessed(page);
err:
    ext4_mb_put_buddy_page_lock(&e4b);
    return ret;
}

/*
 * Locking note:  This routine calls ext4_mb_init_cache(), which takes the
 * block group lock of all groups for this page; do not hold the BG lock when
 * calling this routine!
 */
static noinline_for_stack int
ext4_mb_load_buddy(struct super_block *sb, ext4_group_t group,
                    struct ext4_buddy *e4b)
{
    int blocks_per_page;
    int block;
    int pnum;
    int poff;
    struct page *page;
    int ret;
    struct ext4_group_info *grp;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    struct inode *inode = sbi->s_buddy_cache;

    mb_debug(1, "load group %u\n", group);

    blocks_per_page = PAGE_CACHE_SIZE / sb->s_blocksize;
    grp = ext4_get_group_info(sb, group);

    e4b->bd_blkbits = sb->s_blocksize_bits;
    e4b->bd_info = grp;
    e4b->bd_sb = sb;
    e4b->bd_group = group;
    e4b->bd_buddy_page = NULL;
    e4b->bd_bitmap_page = NULL;

    if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
        /*
         * we need full data about the group
         * to make a good selection
         */
        ret = ext4_mb_init_group(sb, group);
        if (ret)
            return ret;
    }

    /*
     * the buddy cache inode stores the block bitmap
     * and buddy information in consecutive blocks.
     * So for each group we need two blocks.
     */
    block = group * 2;
    pnum = block / blocks_per_page;
    poff = block % blocks_per_page;

    /* we could use find_or_create_page(), but it locks page
     * what we'd like to avoid in fast path ... */
    page = find_get_page(inode->i_mapping, pnum);
    if (page == NULL || !PageUptodate(page)) {
        if (page)
            /*
             * drop the page reference and try
             * to get the page with lock. If we
             * are not uptodate that implies
             * somebody just created the page but
             * is yet to initialize the same. So
             * wait for it to initialize.
             */
            page_cache_release(page);
        page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);
        if (page) {
            BUG_ON(page->mapping != inode->i_mapping);
            if (!PageUptodate(page)) {
                ret = ext4_mb_init_cache(page, NULL);
                if (ret) {
                    unlock_page(page);
                    goto err;
                }
                mb_cmp_bitmaps(e4b, page_address(page) +
                           (poff * sb->s_blocksize));
            }
            unlock_page(page);
        }
    }
    if (page == NULL || !PageUptodate(page)) {
        ret = -EIO;
        goto err;
    }
    e4b->bd_bitmap_page = page;
    e4b->bd_bitmap = page_address(page) + (poff * sb->s_blocksize);
    mark_page_accessed(page);

    block++;
    pnum = block / blocks_per_page;
    poff = block % blocks_per_page;

    page = find_get_page(inode->i_mapping, pnum);
    if (page == NULL || !PageUptodate(page)) {
        if (page)
            page_cache_release(page);
        page = find_or_create_page(inode->i_mapping, pnum, GFP_NOFS);
        if (page) {
            BUG_ON(page->mapping != inode->i_mapping);
            if (!PageUptodate(page)) {
                ret = ext4_mb_init_cache(page, e4b->bd_bitmap);
                if (ret) {
                    unlock_page(page);
                    goto err;
                }
            }
            unlock_page(page);
        }
    }
    if (page == NULL || !PageUptodate(page)) {
        ret = -EIO;
        goto err;
    }
    e4b->bd_buddy_page = page;
    e4b->bd_buddy = page_address(page) + (poff * sb->s_blocksize);
    mark_page_accessed(page);

    BUG_ON(e4b->bd_bitmap_page == NULL);
    BUG_ON(e4b->bd_buddy_page == NULL);

    return 0;

err:
    if (page)
        page_cache_release(page);
    if (e4b->bd_bitmap_page)
        page_cache_release(e4b->bd_bitmap_page);
    if (e4b->bd_buddy_page)
        page_cache_release(e4b->bd_buddy_page);
    e4b->bd_buddy = NULL;
    e4b->bd_bitmap = NULL;
    return ret;
}

static void ext4_mb_unload_buddy(struct ext4_buddy *e4b)
{
    if (e4b->bd_bitmap_page)
        page_cache_release(e4b->bd_bitmap_page);
    if (e4b->bd_buddy_page)
        page_cache_release(e4b->bd_buddy_page);
}


static int mb_find_order_for_block(struct ext4_buddy *e4b, int block)
{
    int order = 1;
    void *bb;

    BUG_ON(e4b->bd_bitmap == e4b->bd_buddy);
    BUG_ON(block >= (1 << (e4b->bd_blkbits + 3)));

    bb = e4b->bd_buddy;
    while (order <= e4b->bd_blkbits + 1) {
        block = block >> 1;
        if (!mb_test_bit(block, bb)) {
            /* this block is part of buddy of order 'order' */
            return order;
        }
        bb += 1 << (e4b->bd_blkbits - order);
        order++;
    }
    return 0;
}

static void mb_clear_bits(void *bm, int cur, int len)
{
    __u32 *addr;

    len = cur + len;
    while (cur < len) {
        if ((cur & 31) == 0 && (len - cur) >= 32) {
            /* fast path: clear whole word at once */
            addr = bm + (cur >> 3);
            *addr = 0;
            cur += 32;
            continue;
        }
        mb_clear_bit(cur, bm);
        cur++;
    }
}

void ext4_set_bits(void *bm, int cur, int len)
{
    __u32 *addr;

    len = cur + len;
    while (cur < len) {
        if ((cur & 31) == 0 && (len - cur) >= 32) {
            /* fast path: set whole word at once */
            addr = bm + (cur >> 3);
            *addr = 0xffffffff;
            cur += 32;
            continue;
        }
        mb_set_bit(cur, bm);
        cur++;
    }
}

static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
              int first, int count)
{
    int block = 0;
    int max = 0;
    int order;
    void *buddy;
    void *buddy2;
    struct super_block *sb = e4b->bd_sb;

    BUG_ON(first + count > (sb->s_blocksize << 3));
    assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
    mb_check_buddy(e4b);
    mb_free_blocks_double(inode, e4b, first, count);

    e4b->bd_info->bb_free += count;
    if (first < e4b->bd_info->bb_first_free)
        e4b->bd_info->bb_first_free = first;

    /* let's maintain fragments counter */
    if (first != 0)
        block = !mb_test_bit(first - 1, e4b->bd_bitmap);
    if (first + count < EXT4_SB(sb)->s_mb_maxs[0])
        max = !mb_test_bit(first + count, e4b->bd_bitmap);
    if (block && max)
        e4b->bd_info->bb_fragments--;
    else if (!block && !max)
        e4b->bd_info->bb_fragments++;

    /* let's maintain buddy itself */
    while (count-- > 0) {
        block = first++;
        order = 0;

        if (!mb_test_bit(block, e4b->bd_bitmap)) {
            ext4_fsblk_t blocknr;

            blocknr = ext4_group_first_block_no(sb, e4b->bd_group);
            blocknr += EXT4_C2B(EXT4_SB(sb), block);
            ext4_grp_locked_error(sb, e4b->bd_group,
                          inode ? inode->i_ino : 0,
                          blocknr,
                          "freeing already freed block "
                          "(bit %u)", block);
        }
        mb_clear_bit(block, e4b->bd_bitmap);
        e4b->bd_info->bb_counters[order]++;

        /* start of the buddy */
        buddy = mb_find_buddy(e4b, order, &max);

        do {
            block &= ~1UL;
            if (mb_test_bit(block, buddy) ||
                    mb_test_bit(block + 1, buddy))
                break;

            /* both the buddies are free, try to coalesce them */
            buddy2 = mb_find_buddy(e4b, order + 1, &max);

            if (!buddy2)
                break;

            if (order > 0) {
                /* for special purposes, we don't set
                 * free bits in bitmap */
                mb_set_bit(block, buddy);
                mb_set_bit(block + 1, buddy);
            }
            e4b->bd_info->bb_counters[order]--;
            e4b->bd_info->bb_counters[order]--;

            block = block >> 1;
            order++;
            e4b->bd_info->bb_counters[order]++;

            mb_clear_bit(block, buddy2);
            buddy = buddy2;
        } while (1);
    }
    mb_set_largest_free_order(sb, e4b->bd_info);
    mb_check_buddy(e4b);
}

static int mb_find_extent(struct ext4_buddy *e4b, int block,
                int needed, struct ext4_free_extent *ex)
{
    int next = block;
    int max, order;
    void *buddy;

    assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
    BUG_ON(ex == NULL);

    buddy = mb_find_buddy(e4b, 0, &max);
    BUG_ON(buddy == NULL);
    BUG_ON(block >= max);
    if (mb_test_bit(block, buddy)) {
        ex->fe_len = 0;
        ex->fe_start = 0;
        ex->fe_group = 0;
        return 0;
    }

    /* find actual order */
    order = mb_find_order_for_block(e4b, block);
    block = block >> order;

    ex->fe_len = 1 << order;
    ex->fe_start = block << order;
    ex->fe_group = e4b->bd_group;

    /* calc difference from given start */
    next = next - ex->fe_start;
    ex->fe_len -= next;
    ex->fe_start += next;

    while (needed > ex->fe_len &&
           (buddy = mb_find_buddy(e4b, order, &max))) {

        if (block + 1 >= max)
            break;

        next = (block + 1) * (1 << order);
        if (mb_test_bit(next, e4b->bd_bitmap))
            break;

        order = mb_find_order_for_block(e4b, next);

        block = next >> order;
        ex->fe_len += 1 << order;
    }

    BUG_ON(ex->fe_start + ex->fe_len > (1 << (e4b->bd_blkbits + 3)));
    return ex->fe_len;
}

static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
{
    int ord;
    int mlen = 0;
    int max = 0;
    int cur;
    int start = ex->fe_start;
    int len = ex->fe_len;
    unsigned ret = 0;
    int len0 = len;
    void *buddy;

    BUG_ON(start + len > (e4b->bd_sb->s_blocksize << 3));
    BUG_ON(e4b->bd_group != ex->fe_group);
    assert_spin_locked(ext4_group_lock_ptr(e4b->bd_sb, e4b->bd_group));
    mb_check_buddy(e4b);
    mb_mark_used_double(e4b, start, len);

    e4b->bd_info->bb_free -= len;
    if (e4b->bd_info->bb_first_free == start)
        e4b->bd_info->bb_first_free += len;

    /* let's maintain fragments counter */
    if (start != 0)
        mlen = !mb_test_bit(start - 1, e4b->bd_bitmap);
    if (start + len < EXT4_SB(e4b->bd_sb)->s_mb_maxs[0])
        max = !mb_test_bit(start + len, e4b->bd_bitmap);
    if (mlen && max)
        e4b->bd_info->bb_fragments++;
    else if (!mlen && !max)
        e4b->bd_info->bb_fragments--;

    /* let's maintain buddy itself */
    while (len) {
        ord = mb_find_order_for_block(e4b, start);

        if (((start >> ord) << ord) == start && len >= (1 << ord)) {
            /* the whole chunk may be allocated at once! */
            mlen = 1 << ord;
            buddy = mb_find_buddy(e4b, ord, &max);
            BUG_ON((start >> ord) >= max);
            mb_set_bit(start >> ord, buddy);
            e4b->bd_info->bb_counters[ord]--;
            start += mlen;
            len -= mlen;
            BUG_ON(len < 0);
            continue;
        }

        /* store for history */
        if (ret == 0)
            ret = len | (ord << 16);

        /* we have to split large buddy */
        BUG_ON(ord <= 0);
        buddy = mb_find_buddy(e4b, ord, &max);
        mb_set_bit(start >> ord, buddy);
        e4b->bd_info->bb_counters[ord]--;

        ord--;
        cur = (start >> ord) & ~1U;
        buddy = mb_find_buddy(e4b, ord, &max);
        mb_clear_bit(cur, buddy);
        mb_clear_bit(cur + 1, buddy);
        e4b->bd_info->bb_counters[ord]++;
        e4b->bd_info->bb_counters[ord]++;
    }
    mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);

    ext4_set_bits(e4b->bd_bitmap, ex->fe_start, len0);
    mb_check_buddy(e4b);

    return ret;
}

/*
 * Must be called under group lock!
 */
static void ext4_mb_use_best_found(struct ext4_allocation_context *ac,
                    struct ext4_buddy *e4b)
{
    struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
    int ret;

    BUG_ON(ac->ac_b_ex.fe_group != e4b->bd_group);
    BUG_ON(ac->ac_status == AC_STATUS_FOUND);

    ac->ac_b_ex.fe_len = min(ac->ac_b_ex.fe_len, ac->ac_g_ex.fe_len);
    ac->ac_b_ex.fe_logical = ac->ac_g_ex.fe_logical;
    ret = mb_mark_used(e4b, &ac->ac_b_ex);

    /* preallocation can change ac_b_ex, thus we store actually
     * allocated blocks for history */
    ac->ac_f_ex = ac->ac_b_ex;

    ac->ac_status = AC_STATUS_FOUND;
    ac->ac_tail = ret & 0xffff;
    ac->ac_buddy = ret >> 16;

    /*
     * take the page reference. We want the page to be pinned
     * so that we don't get a ext4_mb_init_cache_call for this
     * group until we update the bitmap. That would mean we
     * double allocate blocks. The reference is dropped
     * in ext4_mb_release_context
     */
    ac->ac_bitmap_page = e4b->bd_bitmap_page;
    get_page(ac->ac_bitmap_page);
    ac->ac_buddy_page = e4b->bd_buddy_page;
    get_page(ac->ac_buddy_page);
    /* store last allocated for subsequent stream allocation */
    if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
        spin_lock(&sbi->s_md_lock);
        sbi->s_mb_last_group = ac->ac_f_ex.fe_group;
        sbi->s_mb_last_start = ac->ac_f_ex.fe_start;
        spin_unlock(&sbi->s_md_lock);
    }
}

/*
 * regular allocator, for general purposes allocation
 */

static void ext4_mb_check_limits(struct ext4_allocation_context *ac,
                    struct ext4_buddy *e4b,
                    int finish_group)
{
    struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
    struct ext4_free_extent *bex = &ac->ac_b_ex;
    struct ext4_free_extent *gex = &ac->ac_g_ex;
    struct ext4_free_extent ex;
    int max;

    if (ac->ac_status == AC_STATUS_FOUND)
        return;
    /*
     * We don't want to scan for a whole year
     */
    if (ac->ac_found > sbi->s_mb_max_to_scan &&
            !(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
        ac->ac_status = AC_STATUS_BREAK;
        return;
    }

    /*
     * Haven't found good chunk so far, let's continue
     */
    if (bex->fe_len < gex->fe_len)
        return;

    if ((finish_group || ac->ac_found > sbi->s_mb_min_to_scan)
            && bex->fe_group == e4b->bd_group) {
        /* recheck chunk's availability - we don't know
         * when it was found (within this lock-unlock
         * period or not) */
        max = mb_find_extent(e4b, bex->fe_start, gex->fe_len, &ex);
        if (max >= gex->fe_len) {
            ext4_mb_use_best_found(ac, e4b);
            return;
        }
    }
}

/*
 * The routine checks whether found extent is good enough. If it is,
 * then the extent gets marked used and flag is set to the context
 * to stop scanning. Otherwise, the extent is compared with the
 * previous found extent and if new one is better, then it's stored
 * in the context. Later, the best found extent will be used, if
 * mballoc can't find good enough extent.
 *
 * FIXME: real allocation policy is to be designed yet!
 */
static void ext4_mb_measure_extent(struct ext4_allocation_context *ac,
                    struct ext4_free_extent *ex,
                    struct ext4_buddy *e4b)
{
    struct ext4_free_extent *bex = &ac->ac_b_ex;
    struct ext4_free_extent *gex = &ac->ac_g_ex;

    BUG_ON(ex->fe_len <= 0);
    BUG_ON(ex->fe_len > EXT4_CLUSTERS_PER_GROUP(ac->ac_sb));
    BUG_ON(ex->fe_start >= EXT4_CLUSTERS_PER_GROUP(ac->ac_sb));
    BUG_ON(ac->ac_status != AC_STATUS_CONTINUE);

    ac->ac_found++;

    /*
     * The special case - take what you catch first
     */
    if (unlikely(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
        *bex = *ex;
        ext4_mb_use_best_found(ac, e4b);
        return;
    }

    /*
     * Let's check whether the chuck is good enough
     */
    if (ex->fe_len == gex->fe_len) {
        *bex = *ex;
        ext4_mb_use_best_found(ac, e4b);
        return;
    }

    /*
     * If this is first found extent, just store it in the context
     */
    if (bex->fe_len == 0) {
        *bex = *ex;
        return;
    }

    /*
     * If new found extent is better, store it in the context
     */
    if (bex->fe_len < gex->fe_len) {
        /* if the request isn't satisfied, any found extent
         * larger than previous best one is better */
        if (ex->fe_len > bex->fe_len)
            *bex = *ex;
    } else if (ex->fe_len > gex->fe_len) {
        /* if the request is satisfied, then we try to find
         * an extent that still satisfy the request, but is
         * smaller than previous one */
        if (ex->fe_len < bex->fe_len)
            *bex = *ex;
    }

    ext4_mb_check_limits(ac, e4b, 0);
}

static noinline_for_stack
int ext4_mb_try_best_found(struct ext4_allocation_context *ac,
                    struct ext4_buddy *e4b)
{
    struct ext4_free_extent ex = ac->ac_b_ex;
    ext4_group_t group = ex.fe_group;
    int max;
    int err;

    BUG_ON(ex.fe_len <= 0);
    err = ext4_mb_load_buddy(ac->ac_sb, group, e4b);
    if (err)
        return err;

    ext4_lock_group(ac->ac_sb, group);
    max = mb_find_extent(e4b, ex.fe_start, ex.fe_len, &ex);

    if (max > 0) {
        ac->ac_b_ex = ex;
        ext4_mb_use_best_found(ac, e4b);
    }

    ext4_unlock_group(ac->ac_sb, group);
    ext4_mb_unload_buddy(e4b);

    return 0;
}

static noinline_for_stack
int ext4_mb_find_by_goal(struct ext4_allocation_context *ac,
                struct ext4_buddy *e4b)
{
    ext4_group_t group = ac->ac_g_ex.fe_group;
    int max;
    int err;
    struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
    struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
    struct ext4_free_extent ex;

    if (!(ac->ac_flags & EXT4_MB_HINT_TRY_GOAL))
        return 0;
    if (grp->bb_free == 0)
        return 0;

    err = ext4_mb_load_buddy(ac->ac_sb, group, e4b);
    if (err)
        return err;

    ext4_lock_group(ac->ac_sb, group);
    max = mb_find_extent(e4b, ac->ac_g_ex.fe_start,
                 ac->ac_g_ex.fe_len, &ex);

    if (max >= ac->ac_g_ex.fe_len && ac->ac_g_ex.fe_len == sbi->s_stripe) {
        ext4_fsblk_t start;

        start = ext4_group_first_block_no(ac->ac_sb, e4b->bd_group) +
            ex.fe_start;
        /* use do_div to get remainder (would be 64-bit modulo) */
        if (do_div(start, sbi->s_stripe) == 0) {
            ac->ac_found++;
            ac->ac_b_ex = ex;
            ext4_mb_use_best_found(ac, e4b);
        }
    } else if (max >= ac->ac_g_ex.fe_len) {
        BUG_ON(ex.fe_len <= 0);
        BUG_ON(ex.fe_group != ac->ac_g_ex.fe_group);
        BUG_ON(ex.fe_start != ac->ac_g_ex.fe_start);
        ac->ac_found++;
        ac->ac_b_ex = ex;
        ext4_mb_use_best_found(ac, e4b);
    } else if (max > 0 && (ac->ac_flags & EXT4_MB_HINT_MERGE)) {
        /* Sometimes, caller may want to merge even small
         * number of blocks to an existing extent */
        BUG_ON(ex.fe_len <= 0);
        BUG_ON(ex.fe_group != ac->ac_g_ex.fe_group);
        BUG_ON(ex.fe_start != ac->ac_g_ex.fe_start);
        ac->ac_found++;
        ac->ac_b_ex = ex;
        ext4_mb_use_best_found(ac, e4b);
    }
    ext4_unlock_group(ac->ac_sb, group);
    ext4_mb_unload_buddy(e4b);

    return 0;
}

/*
 * The routine scans buddy structures (not bitmap!) from given order
 * to max order and tries to find big enough chunk to satisfy the req
 */
static noinline_for_stack
void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
                    struct ext4_buddy *e4b)
{
    struct super_block *sb = ac->ac_sb;
    struct ext4_group_info *grp = e4b->bd_info;
    void *buddy;
    int i;
    int k;
    int max;

    BUG_ON(ac->ac_2order <= 0);
    for (i = ac->ac_2order; i <= sb->s_blocksize_bits + 1; i++) {
        if (grp->bb_counters[i] == 0)
            continue;

        buddy = mb_find_buddy(e4b, i, &max);
        BUG_ON(buddy == NULL);

        k = mb_find_next_zero_bit(buddy, max, 0);
        BUG_ON(k >= max);

        ac->ac_found++;

        ac->ac_b_ex.fe_len = 1 << i;
        ac->ac_b_ex.fe_start = k << i;
        ac->ac_b_ex.fe_group = e4b->bd_group;

        ext4_mb_use_best_found(ac, e4b);

        BUG_ON(ac->ac_b_ex.fe_len != ac->ac_g_ex.fe_len);

        if (EXT4_SB(sb)->s_mb_stats)
            atomic_inc(&EXT4_SB(sb)->s_bal_2orders);

        break;
    }
}

/*
 * The routine scans the group and measures all found extents.
 * In order to optimize scanning, caller must pass number of
 * free blocks in the group, so the routine can know upper limit.
 */
static noinline_for_stack
void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,
                    struct ext4_buddy *e4b)
{
    struct super_block *sb = ac->ac_sb;
    void *bitmap = e4b->bd_bitmap;
    struct ext4_free_extent ex;
    int i;
    int free;

    free = e4b->bd_info->bb_free;
    BUG_ON(free <= 0);

    i = e4b->bd_info->bb_first_free;

    while (free && ac->ac_status == AC_STATUS_CONTINUE) {
        i = mb_find_next_zero_bit(bitmap,
                        EXT4_CLUSTERS_PER_GROUP(sb), i);
        if (i >= EXT4_CLUSTERS_PER_GROUP(sb)) {
            /*
             * IF we have corrupt bitmap, we won't find any
             * free blocks even though group info says we
             * we have free blocks
             */
            ext4_grp_locked_error(sb, e4b->bd_group, 0, 0,
                    "%d free clusters as per "
                    "group info. But bitmap says 0",
                    free);
            break;
        }

        mb_find_extent(e4b, i, ac->ac_g_ex.fe_len, &ex);
        BUG_ON(ex.fe_len <= 0);
        if (free < ex.fe_len) {
            ext4_grp_locked_error(sb, e4b->bd_group, 0, 0,
                    "%d free clusters as per "
                    "group info. But got %d blocks",
                    free, ex.fe_len);
            /*
             * The number of free blocks differs. This mostly
             * indicate that the bitmap is corrupt. So exit
             * without claiming the space.
             */
            break;
        }

        ext4_mb_measure_extent(ac, &ex, e4b);

        i += ex.fe_len;
        free -= ex.fe_len;
    }

    ext4_mb_check_limits(ac, e4b, 1);
}

/*
 * This is a special case for storages like raid5
 * we try to find stripe-aligned chunks for stripe-size-multiple requests
 */
static noinline_for_stack
void ext4_mb_scan_aligned(struct ext4_allocation_context *ac,
                 struct ext4_buddy *e4b)
{
    struct super_block *sb = ac->ac_sb;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    void *bitmap = e4b->bd_bitmap;
    struct ext4_free_extent ex;
    ext4_fsblk_t first_group_block;
    ext4_fsblk_t a;
    ext4_grpblk_t i;
    int max;

    BUG_ON(sbi->s_stripe == 0);

    /* find first stripe-aligned block in group */
    first_group_block = ext4_group_first_block_no(sb, e4b->bd_group);

    a = first_group_block + sbi->s_stripe - 1;
    do_div(a, sbi->s_stripe);
    i = (a * sbi->s_stripe) - first_group_block;

    while (i < EXT4_CLUSTERS_PER_GROUP(sb)) {
        if (!mb_test_bit(i, bitmap)) {
            max = mb_find_extent(e4b, i, sbi->s_stripe, &ex);
            if (max >= sbi->s_stripe) {
                ac->ac_found++;
                ac->ac_b_ex = ex;
                ext4_mb_use_best_found(ac, e4b);
                break;
            }
        }
        i += sbi->s_stripe;
    }
}

/* This is now called BEFORE we load the buddy bitmap. */
static int ext4_mb_good_group(struct ext4_allocation_context *ac,
                ext4_group_t group, int cr)
{
    unsigned free, fragments;
    int flex_size = ext4_flex_bg_size(EXT4_SB(ac->ac_sb));
    struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);

    BUG_ON(cr < 0 || cr >= 4);

    free = grp->bb_free;
    if (free == 0)
        return 0;
    if (cr <= 2 && free < ac->ac_g_ex.fe_len)
        return 0;

    /* We only do this if the grp has never been initialized */
    if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
        int ret = ext4_mb_init_group(ac->ac_sb, group);
        if (ret)
            return 0;
    }

    fragments = grp->bb_fragments;
    if (fragments == 0)
        return 0;

    switch (cr) {
    case 0:
        BUG_ON(ac->ac_2order == 0);

        if (grp->bb_largest_free_order < ac->ac_2order)
            return 0;

        /* Avoid using the first bg of a flexgroup for data files */
        if ((ac->ac_flags & EXT4_MB_HINT_DATA) &&
            (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) &&
            ((group % flex_size) == 0))
            return 0;

        return 1;
    case 1:
        if ((free / fragments) >= ac->ac_g_ex.fe_len)
            return 1;
        break;
    case 2:
        if (free >= ac->ac_g_ex.fe_len)
            return 1;
        break;
    case 3:
        return 1;
    default:
        BUG();
    }

    return 0;
}

static noinline_for_stack int
ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
{
    ext4_group_t ngroups, group, i;
    int cr;
    int err = 0;
    struct ext4_sb_info *sbi;
    struct super_block *sb;
    struct ext4_buddy e4b;

    sb = ac->ac_sb;
    sbi = EXT4_SB(sb);
    ngroups = ext4_get_groups_count(sb);
    /* non-extent files are limited to low blocks/groups */
    if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)))
        ngroups = sbi->s_blockfile_groups;

    BUG_ON(ac->ac_status == AC_STATUS_FOUND);

    /* first, try the goal */
    err = ext4_mb_find_by_goal(ac, &e4b);
    if (err || ac->ac_status == AC_STATUS_FOUND)
        goto out;

    if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
        goto out;

    /*
     * ac->ac2_order is set only if the fe_len is a power of 2
     * if ac2_order is set we also set criteria to 0 so that we
     * try exact allocation using buddy.
     */
    i = fls(ac->ac_g_ex.fe_len);
    ac->ac_2order = 0;
    /*
     * We search using buddy data only if the order of the request
     * is greater than equal to the sbi_s_mb_order2_reqs
     * You can tune it via /sys/fs/ext4/<partition>/mb_order2_req
     */
    if (i >= sbi->s_mb_order2_reqs) {
        /*
         * This should tell if fe_len is exactly power of 2
         */
        if ((ac->ac_g_ex.fe_len & (~(1 << (i - 1)))) == 0)
            ac->ac_2order = i - 1;
    }

    /* if stream allocation is enabled, use global goal */
    if (ac->ac_flags & EXT4_MB_STREAM_ALLOC) {
        /* TBD: may be hot point */
        spin_lock(&sbi->s_md_lock);
        ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
        ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
        spin_unlock(&sbi->s_md_lock);
    }

    /* Let's just scan groups to find more-less suitable blocks */
    cr = ac->ac_2order ? 0 : 1;
    /*
     * cr == 0 try to get exact allocation,
     * cr == 3  try to get anything
     */
repeat:
    for (; cr < 4 && ac->ac_status == AC_STATUS_CONTINUE; cr++) {
        ac->ac_criteria = cr;
        /*
         * searching for the right group start
         * from the goal value specified
         */
        group = ac->ac_g_ex.fe_group;

        for (i = 0; i < ngroups; group++, i++) {
            if (group == ngroups)
                group = 0;

            /* This now checks without needing the buddy page */
            if (!ext4_mb_good_group(ac, group, cr))
                continue;

            err = ext4_mb_load_buddy(sb, group, &e4b);
            if (err)
                goto out;

            ext4_lock_group(sb, group);

            /*
             * We need to check again after locking the
             * block group
             */
            if (!ext4_mb_good_group(ac, group, cr)) {
                ext4_unlock_group(sb, group);
                ext4_mb_unload_buddy(&e4b);
                continue;
            }

            ac->ac_groups_scanned++;
            if (cr == 0)
                ext4_mb_simple_scan_group(ac, &e4b);
            else if (cr == 1 && sbi->s_stripe &&
                    !(ac->ac_g_ex.fe_len % sbi->s_stripe))
                ext4_mb_scan_aligned(ac, &e4b);
            else
                ext4_mb_complex_scan_group(ac, &e4b);

            ext4_unlock_group(sb, group);
            ext4_mb_unload_buddy(&e4b);

            if (ac->ac_status != AC_STATUS_CONTINUE)
                break;
        }
    }

    if (ac->ac_b_ex.fe_len > 0 && ac->ac_status != AC_STATUS_FOUND &&
        !(ac->ac_flags & EXT4_MB_HINT_FIRST)) {
        /*
         * We've been searching too long. Let's try to allocate
         * the best chunk we've found so far
         */

        ext4_mb_try_best_found(ac, &e4b);
        if (ac->ac_status != AC_STATUS_FOUND) {
            /*
             * Someone more lucky has already allocated it.
             * The only thing we can do is just take first
             * found block(s)
            printk(KERN_DEBUG "EXT4-fs: someone won our chunk\n");
             */
            ac->ac_b_ex.fe_group = 0;
            ac->ac_b_ex.fe_start = 0;
            ac->ac_b_ex.fe_len = 0;
            ac->ac_status = AC_STATUS_CONTINUE;
            ac->ac_flags |= EXT4_MB_HINT_FIRST;
            cr = 3;
            atomic_inc(&sbi->s_mb_lost_chunks);
            goto repeat;
        }
    }
out:
    return err;
}

static void *ext4_mb_seq_groups_start(struct seq_file *seq, loff_t *pos)
{
    struct super_block *sb = seq->private;
    ext4_group_t group;

    if (*pos < 0 || *pos >= ext4_get_groups_count(sb))
        return NULL;
    group = *pos + 1;
    return (void *) ((unsigned long) group);
}

static void *ext4_mb_seq_groups_next(struct seq_file *seq, void *v, loff_t *pos)
{
    struct super_block *sb = seq->private;
    ext4_group_t group;

    ++*pos;
    if (*pos < 0 || *pos >= ext4_get_groups_count(sb))
        return NULL;
    group = *pos + 1;
    return (void *) ((unsigned long) group);
}

static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
{
    struct super_block *sb = seq->private;
    ext4_group_t group = (ext4_group_t) ((unsigned long) v);
    int i;
    int err, buddy_loaded = 0;
    struct ext4_buddy e4b;
    struct ext4_group_info *grinfo;
    struct sg {
        struct ext4_group_info info;
        ext4_grpblk_t counters[16];
    } sg;

    group--;
    if (group == 0)
        seq_printf(seq, "#%-5s: %-5s %-5s %-5s "
                "[ %-5s %-5s %-5s %-5s %-5s %-5s %-5s "
                  "%-5s %-5s %-5s %-5s %-5s %-5s %-5s ]\n",
               "group", "free", "frags", "first",
               "2^0", "2^1", "2^2", "2^3", "2^4", "2^5", "2^6",
               "2^7", "2^8", "2^9", "2^10", "2^11", "2^12", "2^13");

    i = (sb->s_blocksize_bits + 2) * sizeof(sg.info.bb_counters[0]) +
        sizeof(struct ext4_group_info);
    grinfo = ext4_get_group_info(sb, group);
    /* Load the group info in memory only if not already loaded. */
    if (unlikely(EXT4_MB_GRP_NEED_INIT(grinfo))) {
        err = ext4_mb_load_buddy(sb, group, &e4b);
        if (err) {
            seq_printf(seq, "#%-5u: I/O error\n", group);
            return 0;
        }
        buddy_loaded = 1;
    }

    memcpy(&sg, ext4_get_group_info(sb, group), i);

    if (buddy_loaded)
        ext4_mb_unload_buddy(&e4b);

    seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg.info.bb_free,
            sg.info.bb_fragments, sg.info.bb_first_free);
    for (i = 0; i <= 13; i++)
        seq_printf(seq, " %-5u", i <= sb->s_blocksize_bits + 1 ?
                sg.info.bb_counters[i] : 0);
    seq_printf(seq, " ]\n");

    return 0;
}

static void ext4_mb_seq_groups_stop(struct seq_file *seq, void *v)
{
}

static const struct seq_operations ext4_mb_seq_groups_ops = {
    .start  = ext4_mb_seq_groups_start,
    .next   = ext4_mb_seq_groups_next,
    .stop   = ext4_mb_seq_groups_stop,
    .show   = ext4_mb_seq_groups_show,
};

static int ext4_mb_seq_groups_open(struct inode *inode, struct file *file)
{
    struct super_block *sb = PDE(inode)->data;
    int rc;

    rc = seq_open(file, &ext4_mb_seq_groups_ops);
    if (rc == 0) {
        struct seq_file *m = file->private_data;
        m->private = sb;
    }
    return rc;

}

static const struct file_operations ext4_mb_seq_groups_fops = {
    .owner      = THIS_MODULE,
    .open       = ext4_mb_seq_groups_open,
    .read       = seq_read,
    .llseek     = seq_lseek,
    .release    = seq_release,
};

static struct kmem_cache *get_groupinfo_cache(int blocksize_bits)
{
    int cache_index = blocksize_bits - EXT4_MIN_BLOCK_LOG_SIZE;
    struct kmem_cache *cachep = ext4_groupinfo_caches[cache_index];

    BUG_ON(!cachep);
    return cachep;
}

/*
 * Allocate the top-level s_group_info array for the specified number
 * of groups
 */
int ext4_mb_alloc_groupinfo(struct super_block *sb, ext4_group_t ngroups)
{
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    unsigned size;
    struct ext4_group_info ***new_groupinfo;

    size = (ngroups + EXT4_DESC_PER_BLOCK(sb) - 1) >>
        EXT4_DESC_PER_BLOCK_BITS(sb);
    if (size <= sbi->s_group_info_size)
        return 0;

    size = roundup_pow_of_two(sizeof(*sbi->s_group_info) * size);
    new_groupinfo = ext4_kvzalloc(size, GFP_KERNEL);
    if (!new_groupinfo) {
        ext4_msg(sb, KERN_ERR, "can't allocate buddy meta group");
        return -ENOMEM;
    }
    if (sbi->s_group_info) {
        memcpy(new_groupinfo, sbi->s_group_info,
               sbi->s_group_info_size * sizeof(*sbi->s_group_info));
        ext4_kvfree(sbi->s_group_info);
    }
    sbi->s_group_info = new_groupinfo;
    sbi->s_group_info_size = size / sizeof(*sbi->s_group_info);
    ext4_debug("allocated s_groupinfo array for %d meta_bg's\n", 
           sbi->s_group_info_size);
    return 0;
}

/* Create and initialize ext4_group_info data for the given group. */
int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
              struct ext4_group_desc *desc)
{
    int i;
    int metalen = 0;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    struct ext4_group_info **meta_group_info;
    struct kmem_cache *cachep = get_groupinfo_cache(sb->s_blocksize_bits);

    /*
     * First check if this group is the first of a reserved block.
     * If it's true, we have to allocate a new table of pointers
     * to ext4_group_info structures
     */
    if (group % EXT4_DESC_PER_BLOCK(sb) == 0) {
        metalen = sizeof(*meta_group_info) <<
            EXT4_DESC_PER_BLOCK_BITS(sb);
        meta_group_info = kmalloc(metalen, GFP_KERNEL);
        if (meta_group_info == NULL) {
            ext4_msg(sb, KERN_ERR, "can't allocate mem "
                 "for a buddy group");
            goto exit_meta_group_info;
        }
        sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)] =
            meta_group_info;
    }

    meta_group_info =
        sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)];
    i = group & (EXT4_DESC_PER_BLOCK(sb) - 1);

    meta_group_info[i] = kmem_cache_zalloc(cachep, GFP_KERNEL);
    if (meta_group_info[i] == NULL) {
        ext4_msg(sb, KERN_ERR, "can't allocate buddy mem");
        goto exit_group_info;
    }
    set_bit(EXT4_GROUP_INFO_NEED_INIT_BIT,
        &(meta_group_info[i]->bb_state));

    /*
     * initialize bb_free to be able to skip
     * empty groups without initialization
     */
    if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
        meta_group_info[i]->bb_free =
            ext4_free_clusters_after_init(sb, group, desc);
    } else {
        meta_group_info[i]->bb_free =
            ext4_free_group_clusters(sb, desc);
    }

    INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
    init_rwsem(&meta_group_info[i]->alloc_sem);
    meta_group_info[i]->bb_free_root = RB_ROOT;
    meta_group_info[i]->bb_largest_free_order = -1;  /* uninit */

#ifdef DOUBLE_CHECK
    {
        struct buffer_head *bh;
        meta_group_info[i]->bb_bitmap =
            kmalloc(sb->s_blocksize, GFP_KERNEL);
        BUG_ON(meta_group_info[i]->bb_bitmap == NULL);
        bh = ext4_read_block_bitmap(sb, group);
        BUG_ON(bh == NULL);
        memcpy(meta_group_info[i]->bb_bitmap, bh->b_data,
            sb->s_blocksize);
        put_bh(bh);
    }
#endif

    return 0;

exit_group_info:
    /* If a meta_group_info table has been allocated, release it now */
    if (group % EXT4_DESC_PER_BLOCK(sb) == 0) {
        kfree(sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)]);
        sbi->s_group_info[group >> EXT4_DESC_PER_BLOCK_BITS(sb)] = NULL;
    }
exit_meta_group_info:
    return -ENOMEM;
} /* ext4_mb_add_groupinfo */

static int ext4_mb_init_backend(struct super_block *sb)
{
    ext4_group_t ngroups = ext4_get_groups_count(sb);
    ext4_group_t i;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    int err;
    struct ext4_group_desc *desc;
    struct kmem_cache *cachep;

    err = ext4_mb_alloc_groupinfo(sb, ngroups);
    if (err)
        return err;

    sbi->s_buddy_cache = new_inode(sb);
    if (sbi->s_buddy_cache == NULL) {
        ext4_msg(sb, KERN_ERR, "can't get new inode");
        goto err_freesgi;
    }
    /* To avoid potentially colliding with an valid on-disk inode number,
     * use EXT4_BAD_INO for the buddy cache inode number.  This inode is
     * not in the inode hash, so it should never be found by iget(), but
     * this will avoid confusion if it ever shows up during debugging. */
    sbi->s_buddy_cache->i_ino = EXT4_BAD_INO;
    EXT4_I(sbi->s_buddy_cache)->i_disksize = 0;
    for (i = 0; i < ngroups; i++) {
        desc = ext4_get_group_desc(sb, i, NULL);
        if (desc == NULL) {
            ext4_msg(sb, KERN_ERR, "can't read descriptor %u", i);
            goto err_freebuddy;
        }
        if (ext4_mb_add_groupinfo(sb, i, desc) != 0)
            goto err_freebuddy;
    }

    return 0;

err_freebuddy:
    cachep = get_groupinfo_cache(sb->s_blocksize_bits);
    while (i-- > 0)
        kmem_cache_free(cachep, ext4_get_group_info(sb, i));
    i = sbi->s_group_info_size;
    while (i-- > 0)
        kfree(sbi->s_group_info[i]);
    iput(sbi->s_buddy_cache);
err_freesgi:
    ext4_kvfree(sbi->s_group_info);
    return -ENOMEM;
}

static void ext4_groupinfo_destroy_slabs(void)
{
    int i;

    for (i = 0; i < NR_GRPINFO_CACHES; i++) {
        if (ext4_groupinfo_caches[i])
            kmem_cache_destroy(ext4_groupinfo_caches[i]);
        ext4_groupinfo_caches[i] = NULL;
    }
}

static int ext4_groupinfo_create_slab(size_t size)
{
    static DEFINE_MUTEX(ext4_grpinfo_slab_create_mutex);
    int slab_size;
    int blocksize_bits = order_base_2(size);
    int cache_index = blocksize_bits - EXT4_MIN_BLOCK_LOG_SIZE;
    struct kmem_cache *cachep;

    if (cache_index >= NR_GRPINFO_CACHES)
        return -EINVAL;

    if (unlikely(cache_index < 0))
        cache_index = 0;

    mutex_lock(&ext4_grpinfo_slab_create_mutex);
    if (ext4_groupinfo_caches[cache_index]) {
        mutex_unlock(&ext4_grpinfo_slab_create_mutex);
        return 0;   /* Already created */
    }

    slab_size = offsetof(struct ext4_group_info,
                bb_counters[blocksize_bits + 2]);

    cachep = kmem_cache_create(ext4_groupinfo_slab_names[cache_index],
                    slab_size, 0, SLAB_RECLAIM_ACCOUNT,
                    NULL);

    ext4_groupinfo_caches[cache_index] = cachep;

    mutex_unlock(&ext4_grpinfo_slab_create_mutex);
    if (!cachep) {
        printk(KERN_EMERG
               "EXT4-fs: no memory for groupinfo slab cache\n");
        return -ENOMEM;
    }

    return 0;
}

int ext4_mb_init(struct super_block *sb)
{
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    unsigned i, j;
    unsigned offset;
    unsigned max;
    int ret;

    i = (sb->s_blocksize_bits + 2) * sizeof(*sbi->s_mb_offsets);

    sbi->s_mb_offsets = kmalloc(i, GFP_KERNEL);
    if (sbi->s_mb_offsets == NULL) {
        ret = -ENOMEM;
        goto out;
    }

    i = (sb->s_blocksize_bits + 2) * sizeof(*sbi->s_mb_maxs);
    sbi->s_mb_maxs = kmalloc(i, GFP_KERNEL);
    if (sbi->s_mb_maxs == NULL) {
        ret = -ENOMEM;
        goto out;
    }

    ret = ext4_groupinfo_create_slab(sb->s_blocksize);
    if (ret < 0)
        goto out;

    /* order 0 is regular bitmap */
    sbi->s_mb_maxs[0] = sb->s_blocksize << 3;
    sbi->s_mb_offsets[0] = 0;

    i = 1;
    offset = 0;
    max = sb->s_blocksize << 2;
    do {
        sbi->s_mb_offsets[i] = offset;
        sbi->s_mb_maxs[i] = max;
        offset += 1 << (sb->s_blocksize_bits - i);
        max = max >> 1;
        i++;
    } while (i <= sb->s_blocksize_bits + 1);

    spin_lock_init(&sbi->s_md_lock);
    spin_lock_init(&sbi->s_bal_lock);

    sbi->s_mb_max_to_scan = MB_DEFAULT_MAX_TO_SCAN;
    sbi->s_mb_min_to_scan = MB_DEFAULT_MIN_TO_SCAN;
    sbi->s_mb_stats = MB_DEFAULT_STATS;
    sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
    sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
    /*
     * The default group preallocation is 512, which for 4k block
     * sizes translates to 2 megabytes.  However for bigalloc file
     * systems, this is probably too big (i.e, if the cluster size
     * is 1 megabyte, then group preallocation size becomes half a
     * gigabyte!).  As a default, we will keep a two megabyte
     * group pralloc size for cluster sizes up to 64k, and after
     * that, we will force a minimum group preallocation size of
     * 32 clusters.  This translates to 8 megs when the cluster
     * size is 256k, and 32 megs when the cluster size is 1 meg,
     * which seems reasonable as a default.
     */
    sbi->s_mb_group_prealloc = max(MB_DEFAULT_GROUP_PREALLOC >>
                       sbi->s_cluster_bits, 32);
    /*
     * If there is a s_stripe > 1, then we set the s_mb_group_prealloc
     * to the lowest multiple of s_stripe which is bigger than
     * the s_mb_group_prealloc as determined above. We want
     * the preallocation size to be an exact multiple of the
     * RAID stripe size so that preallocations don't fragment
     * the stripes.
     */
    if (sbi->s_stripe > 1) {
        sbi->s_mb_group_prealloc = roundup(
            sbi->s_mb_group_prealloc, sbi->s_stripe);
    }

    sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
    if (sbi->s_locality_groups == NULL) {
        ret = -ENOMEM;
        goto out_free_groupinfo_slab;
    }
    for_each_possible_cpu(i) {
        struct ext4_locality_group *lg;
        lg = per_cpu_ptr(sbi->s_locality_groups, i);
        mutex_init(&lg->lg_mutex);
        for (j = 0; j < PREALLOC_TB_SIZE; j++)
            INIT_LIST_HEAD(&lg->lg_prealloc_list[j]);
        spin_lock_init(&lg->lg_prealloc_lock);
    }

    /* init file for buddy data */
    ret = ext4_mb_init_backend(sb);
    if (ret != 0)
        goto out_free_locality_groups;

    if (sbi->s_proc)
        proc_create_data("mb_groups", S_IRUGO, sbi->s_proc,
                 &ext4_mb_seq_groups_fops, sb);

    return 0;

out_free_locality_groups:
    free_percpu(sbi->s_locality_groups);
    sbi->s_locality_groups = NULL;
out_free_groupinfo_slab:
    ext4_groupinfo_destroy_slabs();
out:
    kfree(sbi->s_mb_offsets);
    sbi->s_mb_offsets = NULL;
    kfree(sbi->s_mb_maxs);
    sbi->s_mb_maxs = NULL;
    return ret;
}

/* need to called with the ext4 group lock held */
static void ext4_mb_cleanup_pa(struct ext4_group_info *grp)
{
    struct ext4_prealloc_space *pa;
    struct list_head *cur, *tmp;
    int count = 0;

    list_for_each_safe(cur, tmp, &grp->bb_prealloc_list) {
        pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
        list_del(&pa->pa_group_list);
        count++;
        kmem_cache_free(ext4_pspace_cachep, pa);
    }
    if (count)
        mb_debug(1, "mballoc: %u PAs left\n", count);

}

int ext4_mb_release(struct super_block *sb)
{
    ext4_group_t ngroups = ext4_get_groups_count(sb);
    ext4_group_t i;
    int num_meta_group_infos;
    struct ext4_group_info *grinfo;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    struct kmem_cache *cachep = get_groupinfo_cache(sb->s_blocksize_bits);

    if (sbi->s_proc)
        remove_proc_entry("mb_groups", sbi->s_proc);

    if (sbi->s_group_info) {
        for (i = 0; i < ngroups; i++) {
            grinfo = ext4_get_group_info(sb, i);
#ifdef DOUBLE_CHECK
            kfree(grinfo->bb_bitmap);
#endif
            ext4_lock_group(sb, i);
            ext4_mb_cleanup_pa(grinfo);
            ext4_unlock_group(sb, i);
            kmem_cache_free(cachep, grinfo);
        }
        num_meta_group_infos = (ngroups +
                EXT4_DESC_PER_BLOCK(sb) - 1) >>
            EXT4_DESC_PER_BLOCK_BITS(sb);
        for (i = 0; i < num_meta_group_infos; i++)
            kfree(sbi->s_group_info[i]);
        ext4_kvfree(sbi->s_group_info);
    }
    kfree(sbi->s_mb_offsets);
    kfree(sbi->s_mb_maxs);
    if (sbi->s_buddy_cache)
        iput(sbi->s_buddy_cache);
    if (sbi->s_mb_stats) {
        ext4_msg(sb, KERN_INFO,
               "mballoc: %u blocks %u reqs (%u success)",
                atomic_read(&sbi->s_bal_allocated),
                atomic_read(&sbi->s_bal_reqs),
                atomic_read(&sbi->s_bal_success));
        ext4_msg(sb, KERN_INFO,
              "mballoc: %u extents scanned, %u goal hits, "
                "%u 2^N hits, %u breaks, %u lost",
                atomic_read(&sbi->s_bal_ex_scanned),
                atomic_read(&sbi->s_bal_goals),
                atomic_read(&sbi->s_bal_2orders),
                atomic_read(&sbi->s_bal_breaks),
                atomic_read(&sbi->s_mb_lost_chunks));
        ext4_msg(sb, KERN_INFO,
               "mballoc: %lu generated and it took %Lu",
                sbi->s_mb_buddies_generated,
                sbi->s_mb_generation_time);
        ext4_msg(sb, KERN_INFO,
               "mballoc: %u preallocated, %u discarded",
                atomic_read(&sbi->s_mb_preallocated),
                atomic_read(&sbi->s_mb_discarded));
    }

    free_percpu(sbi->s_locality_groups);

    return 0;
}

static inline int ext4_issue_discard(struct super_block *sb,
        ext4_group_t block_group, ext4_grpblk_t cluster, int count)
{
    ext4_fsblk_t discard_block;

    discard_block = (EXT4_C2B(EXT4_SB(sb), cluster) +
             ext4_group_first_block_no(sb, block_group));
    count = EXT4_C2B(EXT4_SB(sb), count);
    trace_ext4_discard_blocks(sb,
            (unsigned long long) discard_block, count);
    return sb_issue_discard(sb, discard_block, count, GFP_NOFS, 0);
}

/*
 * This function is called by the jbd2 layer once the commit has finished,
 * so we know we can free the blocks that were released with that commit.
 */
static void ext4_free_data_callback(struct super_block *sb,
                    struct ext4_journal_cb_entry *jce,
                    int rc)
{
    struct ext4_free_data *entry = (struct ext4_free_data *)jce;
    struct ext4_buddy e4b;
    struct ext4_group_info *db;
    int err, count = 0, count2 = 0;

    mb_debug(1, "gonna free %u blocks in group %u (0x%p):",
         entry->efd_count, entry->efd_group, entry);

    if (test_opt(sb, DISCARD))
        ext4_issue_discard(sb, entry->efd_group,
                   entry->efd_start_cluster, entry->efd_count);

    err = ext4_mb_load_buddy(sb, entry->efd_group, &e4b);
    /* we expect to find existing buddy because it's pinned */
    BUG_ON(err != 0);


    db = e4b.bd_info;
    /* there are blocks to put in buddy to make them really free */
    count += entry->efd_count;
    count2++;
    ext4_lock_group(sb, entry->efd_group);
    /* Take it out of per group rb tree */
    rb_erase(&entry->efd_node, &(db->bb_free_root));
    mb_free_blocks(NULL, &e4b, entry->efd_start_cluster, entry->efd_count);

    /*
     * Clear the trimmed flag for the group so that the next
     * ext4_trim_fs can trim it.
     * If the volume is mounted with -o discard, online discard
     * is supported and the free blocks will be trimmed online.
     */
    if (!test_opt(sb, DISCARD))
        EXT4_MB_GRP_CLEAR_TRIMMED(db);

    if (!db->bb_free_root.rb_node) {
        /* No more items in the per group rb tree
         * balance refcounts from ext4_mb_free_metadata()
         */
        page_cache_release(e4b.bd_buddy_page);
        page_cache_release(e4b.bd_bitmap_page);
    }
    ext4_unlock_group(sb, entry->efd_group);
    kmem_cache_free(ext4_free_data_cachep, entry);
    ext4_mb_unload_buddy(&e4b);

    mb_debug(1, "freed %u blocks in %u structures\n", count, count2);
}

#ifdef CONFIG_EXT4_DEBUG
u8 mb_enable_debug __read_mostly;

static struct dentry *debugfs_dir;
static struct dentry *debugfs_debug;

static void __init ext4_create_debugfs_entry(void)
{
    debugfs_dir = debugfs_create_dir("ext4", NULL);
    if (debugfs_dir)
        debugfs_debug = debugfs_create_u8("mballoc-debug",
                          S_IRUGO | S_IWUSR,
                          debugfs_dir,
                          &mb_enable_debug);
}

static void ext4_remove_debugfs_entry(void)
{
    debugfs_remove(debugfs_debug);
    debugfs_remove(debugfs_dir);
}

#else

static void __init ext4_create_debugfs_entry(void)
{
}

static void ext4_remove_debugfs_entry(void)
{
}

#endif

int __init ext4_init_mballoc(void)
{
    ext4_pspace_cachep = KMEM_CACHE(ext4_prealloc_space,
                    SLAB_RECLAIM_ACCOUNT);
    if (ext4_pspace_cachep == NULL)
        return -ENOMEM;

    ext4_ac_cachep = KMEM_CACHE(ext4_allocation_context,
                    SLAB_RECLAIM_ACCOUNT);
    if (ext4_ac_cachep == NULL) {
        kmem_cache_destroy(ext4_pspace_cachep);
        return -ENOMEM;
    }

    ext4_free_data_cachep = KMEM_CACHE(ext4_free_data,
                       SLAB_RECLAIM_ACCOUNT);
    if (ext4_free_data_cachep == NULL) {
        kmem_cache_destroy(ext4_pspace_cachep);
        kmem_cache_destroy(ext4_ac_cachep);
        return -ENOMEM;
    }
    ext4_create_debugfs_entry();
    return 0;
}

void ext4_exit_mballoc(void)
{
    /*
     * Wait for completion of call_rcu()'s on ext4_pspace_cachep
     * before destroying the slab cache.
     */
    rcu_barrier();
    kmem_cache_destroy(ext4_pspace_cachep);
    kmem_cache_destroy(ext4_ac_cachep);
    kmem_cache_destroy(ext4_free_data_cachep);
    ext4_groupinfo_destroy_slabs();
    ext4_remove_debugfs_entry();
}


/*
 * Check quota and mark chosen space (ac->ac_b_ex) non-free in bitmaps
 * Returns 0 if success or error code
 */
static noinline_for_stack int
ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
                handle_t *handle, unsigned int reserv_clstrs)
{
    struct buffer_head *bitmap_bh = NULL;
    struct ext4_group_desc *gdp;
    struct buffer_head *gdp_bh;
    struct ext4_sb_info *sbi;
    struct super_block *sb;
    ext4_fsblk_t block;
    int err, len;

    BUG_ON(ac->ac_status != AC_STATUS_FOUND);
    BUG_ON(ac->ac_b_ex.fe_len <= 0);

    sb = ac->ac_sb;
    sbi = EXT4_SB(sb);

    err = -EIO;
    bitmap_bh = ext4_read_block_bitmap(sb, ac->ac_b_ex.fe_group);
    if (!bitmap_bh)
        goto out_err;

    err = ext4_journal_get_write_access(handle, bitmap_bh);
    if (err)
        goto out_err;

    err = -EIO;
    gdp = ext4_get_group_desc(sb, ac->ac_b_ex.fe_group, &gdp_bh);
    if (!gdp)
        goto out_err;

    ext4_debug("using block group %u(%d)\n", ac->ac_b_ex.fe_group,
            ext4_free_group_clusters(sb, gdp));

    err = ext4_journal_get_write_access(handle, gdp_bh);
    if (err)
        goto out_err;

    block = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);

    len = EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
    if (!ext4_data_block_valid(sbi, block, len)) {
        ext4_error(sb, "Allocating blocks %llu-%llu which overlap "
               "fs metadata", block, block+len);
        /* File system mounted not to panic on error
         * Fix the bitmap and repeat the block allocation
         * We leak some of the blocks here.
         */
        ext4_lock_group(sb, ac->ac_b_ex.fe_group);
        ext4_set_bits(bitmap_bh->b_data, ac->ac_b_ex.fe_start,
                  ac->ac_b_ex.fe_len);
        ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
        err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
        if (!err)
            err = -EAGAIN;
        goto out_err;
    }

    ext4_lock_group(sb, ac->ac_b_ex.fe_group);
#ifdef AGGRESSIVE_CHECK
    {
        int i;
        for (i = 0; i < ac->ac_b_ex.fe_len; i++) {
            BUG_ON(mb_test_bit(ac->ac_b_ex.fe_start + i,
                        bitmap_bh->b_data));
        }
    }
#endif
    ext4_set_bits(bitmap_bh->b_data, ac->ac_b_ex.fe_start,
              ac->ac_b_ex.fe_len);
    if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
        gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
        ext4_free_group_clusters_set(sb, gdp,
                         ext4_free_clusters_after_init(sb,
                        ac->ac_b_ex.fe_group, gdp));
    }
    len = ext4_free_group_clusters(sb, gdp) - ac->ac_b_ex.fe_len;
    ext4_free_group_clusters_set(sb, gdp, len);
    ext4_block_bitmap_csum_set(sb, ac->ac_b_ex.fe_group, gdp, bitmap_bh);
    ext4_group_desc_csum_set(sb, ac->ac_b_ex.fe_group, gdp);

    ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
    percpu_counter_sub(&sbi->s_freeclusters_counter, ac->ac_b_ex.fe_len);
    /*
     * Now reduce the dirty block count also. Should not go negative
     */
    if (!(ac->ac_flags & EXT4_MB_DELALLOC_RESERVED))
        /* release all the reserved blocks if non delalloc */
        percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                   reserv_clstrs);

    if (sbi->s_log_groups_per_flex) {
        ext4_group_t flex_group = ext4_flex_group(sbi,
                              ac->ac_b_ex.fe_group);
        atomic_sub(ac->ac_b_ex.fe_len,
               &sbi->s_flex_groups[flex_group].free_clusters);
    }

    err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
    if (err)
        goto out_err;
    err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);

out_err:
    brelse(bitmap_bh);
    return err;
}

/*
 * here we normalize request for locality group
 * Group request are normalized to s_mb_group_prealloc, which goes to
 * s_strip if we set the same via mount option.
 * s_mb_group_prealloc can be configured via
 * /sys/fs/ext4/<partition>/mb_group_prealloc
 *
 * XXX: should we try to preallocate more than the group has now?
 */
static void ext4_mb_normalize_group_request(struct ext4_allocation_context *ac)
{
    struct super_block *sb = ac->ac_sb;
    struct ext4_locality_group *lg = ac->ac_lg;

    BUG_ON(lg == NULL);
    ac->ac_g_ex.fe_len = EXT4_SB(sb)->s_mb_group_prealloc;
    mb_debug(1, "#%u: goal %u blocks for locality group\n",
        current->pid, ac->ac_g_ex.fe_len);
}

/*
 * Normalization means making request better in terms of
 * size and alignment
 */
static noinline_for_stack void
ext4_mb_normalize_request(struct ext4_allocation_context *ac,
                struct ext4_allocation_request *ar)
{
    struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
    int bsbits, max;
    ext4_lblk_t end;
    loff_t size, start_off;
    loff_t orig_size __maybe_unused;
    ext4_lblk_t start;
    struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
    struct ext4_prealloc_space *pa;

    /* do normalize only data requests, metadata requests
       do not need preallocation */
    if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
        return;

    /* sometime caller may want exact blocks */
    if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
        return;

    /* caller may indicate that preallocation isn't
     * required (it's a tail, for example) */
    if (ac->ac_flags & EXT4_MB_HINT_NOPREALLOC)
        return;

    if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC) {
        ext4_mb_normalize_group_request(ac);
        return ;
    }

    bsbits = ac->ac_sb->s_blocksize_bits;

    /* first, let's learn actual file size
     * given current request is allocated */
    size = ac->ac_o_ex.fe_logical + EXT4_C2B(sbi, ac->ac_o_ex.fe_len);
    size = size << bsbits;
    if (size < i_size_read(ac->ac_inode))
        size = i_size_read(ac->ac_inode);
    orig_size = size;

    /* max size of free chunks */
    max = 2 << bsbits;

#define NRL_CHECK_SIZE(req, size, max, chunk_size)  \
        (req <= (size) || max <= (chunk_size))

    /* first, try to predict filesize */
    /* XXX: should this table be tunable? */
    start_off = 0;
    if (size <= 16 * 1024) {
        size = 16 * 1024;
    } else if (size <= 32 * 1024) {
        size = 32 * 1024;
    } else if (size <= 64 * 1024) {
        size = 64 * 1024;
    } else if (size <= 128 * 1024) {
        size = 128 * 1024;
    } else if (size <= 256 * 1024) {
        size = 256 * 1024;
    } else if (size <= 512 * 1024) {
        size = 512 * 1024;
    } else if (size <= 1024 * 1024) {
        size = 1024 * 1024;
    } else if (NRL_CHECK_SIZE(size, 4 * 1024 * 1024, max, 2 * 1024)) {
        start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
                        (21 - bsbits)) << 21;
        size = 2 * 1024 * 1024;
    } else if (NRL_CHECK_SIZE(size, 8 * 1024 * 1024, max, 4 * 1024)) {
        start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
                            (22 - bsbits)) << 22;
        size = 4 * 1024 * 1024;
    } else if (NRL_CHECK_SIZE(ac->ac_o_ex.fe_len,
                    (8<<20)>>bsbits, max, 8 * 1024)) {
        start_off = ((loff_t)ac->ac_o_ex.fe_logical >>
                            (23 - bsbits)) << 23;
        size = 8 * 1024 * 1024;
    } else {
        start_off = (loff_t)ac->ac_o_ex.fe_logical << bsbits;
        size      = ac->ac_o_ex.fe_len << bsbits;
    }
    size = size >> bsbits;
    start = start_off >> bsbits;

    /* don't cover already allocated blocks in selected range */
    if (ar->pleft && start <= ar->lleft) {
        size -= ar->lleft + 1 - start;
        start = ar->lleft + 1;
    }
    if (ar->pright && start + size - 1 >= ar->lright)
        size -= start + size - ar->lright;

    end = start + size;

    /* check we don't cross already preallocated blocks */
    rcu_read_lock();
    list_for_each_entry_rcu(pa, &ei->i_prealloc_list, pa_inode_list) {
        ext4_lblk_t pa_end;

        if (pa->pa_deleted)
            continue;
        spin_lock(&pa->pa_lock);
        if (pa->pa_deleted) {
            spin_unlock(&pa->pa_lock);
            continue;
        }

        pa_end = pa->pa_lstart + EXT4_C2B(EXT4_SB(ac->ac_sb),
                          pa->pa_len);

        /* PA must not overlap original request */
        BUG_ON(!(ac->ac_o_ex.fe_logical >= pa_end ||
            ac->ac_o_ex.fe_logical < pa->pa_lstart));

        /* skip PAs this normalized request doesn't overlap with */
        if (pa->pa_lstart >= end || pa_end <= start) {
            spin_unlock(&pa->pa_lock);
            continue;
        }
        BUG_ON(pa->pa_lstart <= start && pa_end >= end);

        /* adjust start or end to be adjacent to this pa */
        if (pa_end <= ac->ac_o_ex.fe_logical) {
            BUG_ON(pa_end < start);
            start = pa_end;
        } else if (pa->pa_lstart > ac->ac_o_ex.fe_logical) {
            BUG_ON(pa->pa_lstart > end);
            end = pa->pa_lstart;
        }
        spin_unlock(&pa->pa_lock);
    }
    rcu_read_unlock();
    size = end - start;

    /* XXX: extra loop to check we really don't overlap preallocations */
    rcu_read_lock();
    list_for_each_entry_rcu(pa, &ei->i_prealloc_list, pa_inode_list) {
        ext4_lblk_t pa_end;

        spin_lock(&pa->pa_lock);
        if (pa->pa_deleted == 0) {
            pa_end = pa->pa_lstart + EXT4_C2B(EXT4_SB(ac->ac_sb),
                              pa->pa_len);
            BUG_ON(!(start >= pa_end || end <= pa->pa_lstart));
        }
        spin_unlock(&pa->pa_lock);
    }
    rcu_read_unlock();

    if (start + size <= ac->ac_o_ex.fe_logical &&
            start > ac->ac_o_ex.fe_logical) {
        ext4_msg(ac->ac_sb, KERN_ERR,
             "start %lu, size %lu, fe_logical %lu",
             (unsigned long) start, (unsigned long) size,
             (unsigned long) ac->ac_o_ex.fe_logical);
    }
    BUG_ON(start + size <= ac->ac_o_ex.fe_logical &&
            start > ac->ac_o_ex.fe_logical);
    BUG_ON(size <= 0 || size > EXT4_CLUSTERS_PER_GROUP(ac->ac_sb));

    /* now prepare goal request */

    /* XXX: is it better to align blocks WRT to logical
     * placement or satisfy big request as is */
    ac->ac_g_ex.fe_logical = start;
    ac->ac_g_ex.fe_len = EXT4_NUM_B2C(sbi, size);

    /* define goal start in order to merge */
    if (ar->pright && (ar->lright == (start + size))) {
        /* merge to the right */
        ext4_get_group_no_and_offset(ac->ac_sb, ar->pright - size,
                        &ac->ac_f_ex.fe_group,
                        &ac->ac_f_ex.fe_start);
        ac->ac_flags |= EXT4_MB_HINT_TRY_GOAL;
    }
    if (ar->pleft && (ar->lleft + 1 == start)) {
        /* merge to the left */
        ext4_get_group_no_and_offset(ac->ac_sb, ar->pleft + 1,
                        &ac->ac_f_ex.fe_group,
                        &ac->ac_f_ex.fe_start);
        ac->ac_flags |= EXT4_MB_HINT_TRY_GOAL;
    }

    mb_debug(1, "goal: %u(was %u) blocks at %u\n", (unsigned) size,
        (unsigned) orig_size, (unsigned) start);
}

static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
{
    struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);

    if (sbi->s_mb_stats && ac->ac_g_ex.fe_len > 1) {
        atomic_inc(&sbi->s_bal_reqs);
        atomic_add(ac->ac_b_ex.fe_len, &sbi->s_bal_allocated);
        if (ac->ac_b_ex.fe_len >= ac->ac_o_ex.fe_len)
            atomic_inc(&sbi->s_bal_success);
        atomic_add(ac->ac_found, &sbi->s_bal_ex_scanned);
        if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
                ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)
            atomic_inc(&sbi->s_bal_goals);
        if (ac->ac_found > sbi->s_mb_max_to_scan)
            atomic_inc(&sbi->s_bal_breaks);
    }

    if (ac->ac_op == EXT4_MB_HISTORY_ALLOC)
        trace_ext4_mballoc_alloc(ac);
    else
        trace_ext4_mballoc_prealloc(ac);
}

/*
 * Called on failure; free up any blocks from the inode PA for this
 * context.  We don't need this for MB_GROUP_PA because we only change
 * pa_free in ext4_mb_release_context(), but on failure, we've already
 * zeroed out ac->ac_b_ex.fe_len, so group_pa->pa_free is not changed.
 */
static void ext4_discard_allocated_blocks(struct ext4_allocation_context *ac)
{
    struct ext4_prealloc_space *pa = ac->ac_pa;

    if (pa && pa->pa_type == MB_INODE_PA)
        pa->pa_free += ac->ac_b_ex.fe_len;
}

/*
 * use blocks preallocated to inode
 */
static void ext4_mb_use_inode_pa(struct ext4_allocation_context *ac,
                struct ext4_prealloc_space *pa)
{
    struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
    ext4_fsblk_t start;
    ext4_fsblk_t end;
    int len;

    /* found preallocated blocks, use them */
    start = pa->pa_pstart + (ac->ac_o_ex.fe_logical - pa->pa_lstart);
    end = min(pa->pa_pstart + EXT4_C2B(sbi, pa->pa_len),
          start + EXT4_C2B(sbi, ac->ac_o_ex.fe_len));
    len = EXT4_NUM_B2C(sbi, end - start);
    ext4_get_group_no_and_offset(ac->ac_sb, start, &ac->ac_b_ex.fe_group,
                    &ac->ac_b_ex.fe_start);
    ac->ac_b_ex.fe_len = len;
    ac->ac_status = AC_STATUS_FOUND;
    ac->ac_pa = pa;

    BUG_ON(start < pa->pa_pstart);
    BUG_ON(end > pa->pa_pstart + EXT4_C2B(sbi, pa->pa_len));
    BUG_ON(pa->pa_free < len);
    pa->pa_free -= len;

    mb_debug(1, "use %llu/%u from inode pa %p\n", start, len, pa);
}

/*
 * use blocks preallocated to locality group
 */
static void ext4_mb_use_group_pa(struct ext4_allocation_context *ac,
                struct ext4_prealloc_space *pa)
{
    unsigned int len = ac->ac_o_ex.fe_len;

    ext4_get_group_no_and_offset(ac->ac_sb, pa->pa_pstart,
                    &ac->ac_b_ex.fe_group,
                    &ac->ac_b_ex.fe_start);
    ac->ac_b_ex.fe_len = len;
    ac->ac_status = AC_STATUS_FOUND;
    ac->ac_pa = pa;

    /* we don't correct pa_pstart or pa_plen here to avoid
     * possible race when the group is being loaded concurrently
     * instead we correct pa later, after blocks are marked
     * in on-disk bitmap -- see ext4_mb_release_context()
     * Other CPUs are prevented from allocating from this pa by lg_mutex
     */
    mb_debug(1, "use %u/%u from group pa %p\n", pa->pa_lstart-len, len, pa);
}

/*
 * Return the prealloc space that have minimal distance
 * from the goal block. @cpa is the prealloc
 * space that is having currently known minimal distance
 * from the goal block.
 */
static struct ext4_prealloc_space *
ext4_mb_check_group_pa(ext4_fsblk_t goal_block,
            struct ext4_prealloc_space *pa,
            struct ext4_prealloc_space *cpa)
{
    ext4_fsblk_t cur_distance, new_distance;

    if (cpa == NULL) {
        atomic_inc(&pa->pa_count);
        return pa;
    }
    cur_distance = abs(goal_block - cpa->pa_pstart);
    new_distance = abs(goal_block - pa->pa_pstart);

    if (cur_distance <= new_distance)
        return cpa;

    /* drop the previous reference */
    atomic_dec(&cpa->pa_count);
    atomic_inc(&pa->pa_count);
    return pa;
}

/*
 * search goal blocks in preallocated space
 */
static noinline_for_stack int
ext4_mb_use_preallocated(struct ext4_allocation_context *ac)
{
    struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
    int order, i;
    struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
    struct ext4_locality_group *lg;
    struct ext4_prealloc_space *pa, *cpa = NULL;
    ext4_fsblk_t goal_block;

    /* only data can be preallocated */
    if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
        return 0;

    /* first, try per-file preallocation */
    rcu_read_lock();
    list_for_each_entry_rcu(pa, &ei->i_prealloc_list, pa_inode_list) {

        /* all fields in this condition don't change,
         * so we can skip locking for them */
        if (ac->ac_o_ex.fe_logical < pa->pa_lstart ||
            ac->ac_o_ex.fe_logical >= (pa->pa_lstart +
                           EXT4_C2B(sbi, pa->pa_len)))
            continue;

        /* non-extent files can't have physical blocks past 2^32 */
        if (!(ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS)) &&
            (pa->pa_pstart + EXT4_C2B(sbi, pa->pa_len) >
             EXT4_MAX_BLOCK_FILE_PHYS))
            continue;

        /* found preallocated blocks, use them */
        spin_lock(&pa->pa_lock);
        if (pa->pa_deleted == 0 && pa->pa_free) {
            atomic_inc(&pa->pa_count);
            ext4_mb_use_inode_pa(ac, pa);
            spin_unlock(&pa->pa_lock);
            ac->ac_criteria = 10;
            rcu_read_unlock();
            return 1;
        }
        spin_unlock(&pa->pa_lock);
    }
    rcu_read_unlock();

    /* can we use group allocation? */
    if (!(ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC))
        return 0;

    /* inode may have no locality group for some reason */
    lg = ac->ac_lg;
    if (lg == NULL)
        return 0;
    order  = fls(ac->ac_o_ex.fe_len) - 1;
    if (order > PREALLOC_TB_SIZE - 1)
        /* The max size of hash table is PREALLOC_TB_SIZE */
        order = PREALLOC_TB_SIZE - 1;

    goal_block = ext4_grp_offs_to_block(ac->ac_sb, &ac->ac_g_ex);
    /*
     * search for the prealloc space that is having
     * minimal distance from the goal block.
     */
    for (i = order; i < PREALLOC_TB_SIZE; i++) {
        rcu_read_lock();
        list_for_each_entry_rcu(pa, &lg->lg_prealloc_list[i],
                    pa_inode_list) {
            spin_lock(&pa->pa_lock);
            if (pa->pa_deleted == 0 &&
                    pa->pa_free >= ac->ac_o_ex.fe_len) {

                cpa = ext4_mb_check_group_pa(goal_block,
                                pa, cpa);
            }
            spin_unlock(&pa->pa_lock);
        }
        rcu_read_unlock();
    }
    if (cpa) {
        ext4_mb_use_group_pa(ac, cpa);
        ac->ac_criteria = 20;
        return 1;
    }
    return 0;
}

/*
 * the function goes through all block freed in the group
 * but not yet committed and marks them used in in-core bitmap.
 * buddy must be generated from this bitmap
 * Need to be called with the ext4 group lock held
 */
static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
                        ext4_group_t group)
{
    struct rb_node *n;
    struct ext4_group_info *grp;
    struct ext4_free_data *entry;

    grp = ext4_get_group_info(sb, group);
    n = rb_first(&(grp->bb_free_root));

    while (n) {
        entry = rb_entry(n, struct ext4_free_data, efd_node);
        ext4_set_bits(bitmap, entry->efd_start_cluster, entry->efd_count);
        n = rb_next(n);
    }
    return;
}

/*
 * the function goes through all preallocation in this group and marks them
 * used in in-core bitmap. buddy must be generated from this bitmap
 * Need to be called with ext4 group lock held
 */
static noinline_for_stack
void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
                    ext4_group_t group)
{
    struct ext4_group_info *grp = ext4_get_group_info(sb, group);
    struct ext4_prealloc_space *pa;
    struct list_head *cur;
    ext4_group_t groupnr;
    ext4_grpblk_t start;
    int preallocated = 0;
    int len;

    /* all form of preallocation discards first load group,
     * so the only competing code is preallocation use.
     * we don't need any locking here
     * notice we do NOT ignore preallocations with pa_deleted
     * otherwise we could leave used blocks available for
     * allocation in buddy when concurrent ext4_mb_put_pa()
     * is dropping preallocation
     */
    list_for_each(cur, &grp->bb_prealloc_list) {
        pa = list_entry(cur, struct ext4_prealloc_space, pa_group_list);
        spin_lock(&pa->pa_lock);
        ext4_get_group_no_and_offset(sb, pa->pa_pstart,
                         &groupnr, &start);
        len = pa->pa_len;
        spin_unlock(&pa->pa_lock);
        if (unlikely(len == 0))
            continue;
        BUG_ON(groupnr != group);
        ext4_set_bits(bitmap, start, len);
        preallocated += len;
    }
    mb_debug(1, "prellocated %u for group %u\n", preallocated, group);
}

static void ext4_mb_pa_callback(struct rcu_head *head)
{
    struct ext4_prealloc_space *pa;
    pa = container_of(head, struct ext4_prealloc_space, u.pa_rcu);
    kmem_cache_free(ext4_pspace_cachep, pa);
}

/*
 * drops a reference to preallocated space descriptor
 * if this was the last reference and the space is consumed
 */
static void ext4_mb_put_pa(struct ext4_allocation_context *ac,
            struct super_block *sb, struct ext4_prealloc_space *pa)
{
    ext4_group_t grp;
    ext4_fsblk_t grp_blk;

    if (!atomic_dec_and_test(&pa->pa_count) || pa->pa_free != 0)
        return;

    /* in this short window concurrent discard can set pa_deleted */
    spin_lock(&pa->pa_lock);
    if (pa->pa_deleted == 1) {
        spin_unlock(&pa->pa_lock);
        return;
    }

    pa->pa_deleted = 1;
    spin_unlock(&pa->pa_lock);

    grp_blk = pa->pa_pstart;
    /*
     * If doing group-based preallocation, pa_pstart may be in the
     * next group when pa is used up
     */
    if (pa->pa_type == MB_GROUP_PA)
        grp_blk--;

    ext4_get_group_no_and_offset(sb, grp_blk, &grp, NULL);

    /*
     * possible race:
     *
     *  P1 (buddy init)         P2 (regular allocation)
     *                  find block B in PA
     *  copy on-disk bitmap to buddy
     *                      mark B in on-disk bitmap
     *                  drop PA from group
     *  mark all PAs in buddy
     *
     * thus, P1 initializes buddy with B available. to prevent this
     * we make "copy" and "mark all PAs" atomic and serialize "drop PA"
     * against that pair
     */
    ext4_lock_group(sb, grp);
    list_del(&pa->pa_group_list);
    ext4_unlock_group(sb, grp);

    spin_lock(pa->pa_obj_lock);
    list_del_rcu(&pa->pa_inode_list);
    spin_unlock(pa->pa_obj_lock);

    call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
}

/*
 * creates new preallocated space for given inode
 */
static noinline_for_stack int
ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
{
    struct super_block *sb = ac->ac_sb;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    struct ext4_prealloc_space *pa;
    struct ext4_group_info *grp;
    struct ext4_inode_info *ei;

    /* preallocate only when found space is larger then requested */
    BUG_ON(ac->ac_o_ex.fe_len >= ac->ac_b_ex.fe_len);
    BUG_ON(ac->ac_status != AC_STATUS_FOUND);
    BUG_ON(!S_ISREG(ac->ac_inode->i_mode));

    pa = kmem_cache_alloc(ext4_pspace_cachep, GFP_NOFS);
    if (pa == NULL)
        return -ENOMEM;

    if (ac->ac_b_ex.fe_len < ac->ac_g_ex.fe_len) {
        int winl;
        int wins;
        int win;
        int offs;

        /* we can't allocate as much as normalizer wants.
         * so, found space must get proper lstart
         * to cover original request */
        BUG_ON(ac->ac_g_ex.fe_logical > ac->ac_o_ex.fe_logical);
        BUG_ON(ac->ac_g_ex.fe_len < ac->ac_o_ex.fe_len);

        /* we're limited by original request in that
         * logical block must be covered any way
         * winl is window we can move our chunk within */
        winl = ac->ac_o_ex.fe_logical - ac->ac_g_ex.fe_logical;

        /* also, we should cover whole original request */
        wins = EXT4_C2B(sbi, ac->ac_b_ex.fe_len - ac->ac_o_ex.fe_len);

        /* the smallest one defines real window */
        win = min(winl, wins);

        offs = ac->ac_o_ex.fe_logical %
            EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
        if (offs && offs < win)
            win = offs;

        ac->ac_b_ex.fe_logical = ac->ac_o_ex.fe_logical -
            EXT4_B2C(sbi, win);
        BUG_ON(ac->ac_o_ex.fe_logical < ac->ac_b_ex.fe_logical);
        BUG_ON(ac->ac_o_ex.fe_len > ac->ac_b_ex.fe_len);
    }

    /* preallocation can change ac_b_ex, thus we store actually
     * allocated blocks for history */
    ac->ac_f_ex = ac->ac_b_ex;

    pa->pa_lstart = ac->ac_b_ex.fe_logical;
    pa->pa_pstart = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
    pa->pa_len = ac->ac_b_ex.fe_len;
    pa->pa_free = pa->pa_len;
    atomic_set(&pa->pa_count, 1);
    spin_lock_init(&pa->pa_lock);
    INIT_LIST_HEAD(&pa->pa_inode_list);
    INIT_LIST_HEAD(&pa->pa_group_list);
    pa->pa_deleted = 0;
    pa->pa_type = MB_INODE_PA;

    mb_debug(1, "new inode pa %p: %llu/%u for %u\n", pa,
            pa->pa_pstart, pa->pa_len, pa->pa_lstart);
    trace_ext4_mb_new_inode_pa(ac, pa);

    ext4_mb_use_inode_pa(ac, pa);
    atomic_add(pa->pa_free, &sbi->s_mb_preallocated);

    ei = EXT4_I(ac->ac_inode);
    grp = ext4_get_group_info(sb, ac->ac_b_ex.fe_group);

    pa->pa_obj_lock = &ei->i_prealloc_lock;
    pa->pa_inode = ac->ac_inode;

    ext4_lock_group(sb, ac->ac_b_ex.fe_group);
    list_add(&pa->pa_group_list, &grp->bb_prealloc_list);
    ext4_unlock_group(sb, ac->ac_b_ex.fe_group);

    spin_lock(pa->pa_obj_lock);
    list_add_rcu(&pa->pa_inode_list, &ei->i_prealloc_list);
    spin_unlock(pa->pa_obj_lock);

    return 0;
}

/*
 * creates new preallocated space for locality group inodes belongs to
 */
static noinline_for_stack int
ext4_mb_new_group_pa(struct ext4_allocation_context *ac)
{
    struct super_block *sb = ac->ac_sb;
    struct ext4_locality_group *lg;
    struct ext4_prealloc_space *pa;
    struct ext4_group_info *grp;

    /* preallocate only when found space is larger then requested */
    BUG_ON(ac->ac_o_ex.fe_len >= ac->ac_b_ex.fe_len);
    BUG_ON(ac->ac_status != AC_STATUS_FOUND);
    BUG_ON(!S_ISREG(ac->ac_inode->i_mode));

    BUG_ON(ext4_pspace_cachep == NULL);
    pa = kmem_cache_alloc(ext4_pspace_cachep, GFP_NOFS);
    if (pa == NULL)
        return -ENOMEM;

    /* preallocation can change ac_b_ex, thus we store actually
     * allocated blocks for history */
    ac->ac_f_ex = ac->ac_b_ex;

    pa->pa_pstart = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
    pa->pa_lstart = pa->pa_pstart;
    pa->pa_len = ac->ac_b_ex.fe_len;
    pa->pa_free = pa->pa_len;
    atomic_set(&pa->pa_count, 1);
    spin_lock_init(&pa->pa_lock);
    INIT_LIST_HEAD(&pa->pa_inode_list);
    INIT_LIST_HEAD(&pa->pa_group_list);
    pa->pa_deleted = 0;
    pa->pa_type = MB_GROUP_PA;

    mb_debug(1, "new group pa %p: %llu/%u for %u\n", pa,
            pa->pa_pstart, pa->pa_len, pa->pa_lstart);
    trace_ext4_mb_new_group_pa(ac, pa);

    ext4_mb_use_group_pa(ac, pa);
    atomic_add(pa->pa_free, &EXT4_SB(sb)->s_mb_preallocated);

    grp = ext4_get_group_info(sb, ac->ac_b_ex.fe_group);
    lg = ac->ac_lg;
    BUG_ON(lg == NULL);

    pa->pa_obj_lock = &lg->lg_prealloc_lock;
    pa->pa_inode = NULL;

    ext4_lock_group(sb, ac->ac_b_ex.fe_group);
    list_add(&pa->pa_group_list, &grp->bb_prealloc_list);
    ext4_unlock_group(sb, ac->ac_b_ex.fe_group);

    /*
     * We will later add the new pa to the right bucket
     * after updating the pa_free in ext4_mb_release_context
     */
    return 0;
}

static int ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
{
    int err;

    if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
        err = ext4_mb_new_group_pa(ac);
    else
        err = ext4_mb_new_inode_pa(ac);
    return err;
}

/*
 * finds all unused blocks in on-disk bitmap, frees them in
 * in-core bitmap and buddy.
 * @pa must be unlinked from inode and group lists, so that
 * nobody else can find/use it.
 * the caller MUST hold group/inode locks.
 * TODO: optimize the case when there are no in-core structures yet
 */
static noinline_for_stack int
ext4_mb_release_inode_pa(struct ext4_buddy *e4b, struct buffer_head *bitmap_bh,
            struct ext4_prealloc_space *pa)
{
    struct super_block *sb = e4b->bd_sb;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    unsigned int end;
    unsigned int next;
    ext4_group_t group;
    ext4_grpblk_t bit;
    unsigned long long grp_blk_start;
    int err = 0;
    int free = 0;

    BUG_ON(pa->pa_deleted == 0);
    ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, &bit);
    grp_blk_start = pa->pa_pstart - EXT4_C2B(sbi, bit);
    BUG_ON(group != e4b->bd_group && pa->pa_len != 0);
    end = bit + pa->pa_len;

    while (bit < end) {
        bit = mb_find_next_zero_bit(bitmap_bh->b_data, end, bit);
        if (bit >= end)
            break;
        next = mb_find_next_bit(bitmap_bh->b_data, end, bit);
        mb_debug(1, "    free preallocated %u/%u in group %u\n",
             (unsigned) ext4_group_first_block_no(sb, group) + bit,
             (unsigned) next - bit, (unsigned) group);
        free += next - bit;

        trace_ext4_mballoc_discard(sb, NULL, group, bit, next - bit);
        trace_ext4_mb_release_inode_pa(pa, (grp_blk_start +
                            EXT4_C2B(sbi, bit)),
                           next - bit);
        mb_free_blocks(pa->pa_inode, e4b, bit, next - bit);
        bit = next + 1;
    }
    if (free != pa->pa_free) {
        ext4_msg(e4b->bd_sb, KERN_CRIT,
             "pa %p: logic %lu, phys. %lu, len %lu",
             pa, (unsigned long) pa->pa_lstart,
             (unsigned long) pa->pa_pstart,
             (unsigned long) pa->pa_len);
        ext4_grp_locked_error(sb, group, 0, 0, "free %u, pa_free %u",
                    free, pa->pa_free);
        /*
         * pa is already deleted so we use the value obtained
         * from the bitmap and continue.
         */
    }
    atomic_add(free, &sbi->s_mb_discarded);

    return err;
}

static noinline_for_stack int
ext4_mb_release_group_pa(struct ext4_buddy *e4b,
                struct ext4_prealloc_space *pa)
{
    struct super_block *sb = e4b->bd_sb;
    ext4_group_t group;
    ext4_grpblk_t bit;

    trace_ext4_mb_release_group_pa(sb, pa);
    BUG_ON(pa->pa_deleted == 0);
    ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, &bit);
    BUG_ON(group != e4b->bd_group && pa->pa_len != 0);
    mb_free_blocks(pa->pa_inode, e4b, bit, pa->pa_len);
    atomic_add(pa->pa_len, &EXT4_SB(sb)->s_mb_discarded);
    trace_ext4_mballoc_discard(sb, NULL, group, bit, pa->pa_len);

    return 0;
}

/*
 * releases all preallocations in given group
 *
 * first, we need to decide discard policy:
 * - when do we discard
 *   1) ENOSPC
 * - how many do we discard
 *   1) how many requested
 */
static noinline_for_stack int
ext4_mb_discard_group_preallocations(struct super_block *sb,
                    ext4_group_t group, int needed)
{
    struct ext4_group_info *grp = ext4_get_group_info(sb, group);
    struct buffer_head *bitmap_bh = NULL;
    struct ext4_prealloc_space *pa, *tmp;
    struct list_head list;
    struct ext4_buddy e4b;
    int err;
    int busy = 0;
    int free = 0;

    mb_debug(1, "discard preallocation for group %u\n", group);

    if (list_empty(&grp->bb_prealloc_list))
        return 0;

    bitmap_bh = ext4_read_block_bitmap(sb, group);
    if (bitmap_bh == NULL) {
        ext4_error(sb, "Error reading block bitmap for %u", group);
        return 0;
    }

    err = ext4_mb_load_buddy(sb, group, &e4b);
    if (err) {
        ext4_error(sb, "Error loading buddy information for %u", group);
        put_bh(bitmap_bh);
        return 0;
    }

    if (needed == 0)
        needed = EXT4_CLUSTERS_PER_GROUP(sb) + 1;

    INIT_LIST_HEAD(&list);
repeat:
    ext4_lock_group(sb, group);
    list_for_each_entry_safe(pa, tmp,
                &grp->bb_prealloc_list, pa_group_list) {
        spin_lock(&pa->pa_lock);
        if (atomic_read(&pa->pa_count)) {
            spin_unlock(&pa->pa_lock);
            busy = 1;
            continue;
        }
        if (pa->pa_deleted) {
            spin_unlock(&pa->pa_lock);
            continue;
        }

        /* seems this one can be freed ... */
        pa->pa_deleted = 1;

        /* we can trust pa_free ... */
        free += pa->pa_free;

        spin_unlock(&pa->pa_lock);

        list_del(&pa->pa_group_list);
        list_add(&pa->u.pa_tmp_list, &list);
    }

    /* if we still need more blocks and some PAs were used, try again */
    if (free < needed && busy) {
        busy = 0;
        ext4_unlock_group(sb, group);
        /*
         * Yield the CPU here so that we don't get soft lockup
         * in non preempt case.
         */
        yield();
        goto repeat;
    }

    /* found anything to free? */
    if (list_empty(&list)) {
        BUG_ON(free != 0);
        goto out;
    }

    /* now free all selected PAs */
    list_for_each_entry_safe(pa, tmp, &list, u.pa_tmp_list) {

        /* remove from object (inode or locality group) */
        spin_lock(pa->pa_obj_lock);
        list_del_rcu(&pa->pa_inode_list);
        spin_unlock(pa->pa_obj_lock);

        if (pa->pa_type == MB_GROUP_PA)
            ext4_mb_release_group_pa(&e4b, pa);
        else
            ext4_mb_release_inode_pa(&e4b, bitmap_bh, pa);

        list_del(&pa->u.pa_tmp_list);
        call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
    }

out:
    ext4_unlock_group(sb, group);
    ext4_mb_unload_buddy(&e4b);
    put_bh(bitmap_bh);
    return free;
}

/*
 * releases all non-used preallocated blocks for given inode
 *
 * It's important to discard preallocations under i_data_sem
 * We don't want another block to be served from the prealloc
 * space when we are discarding the inode prealloc space.
 *
 * FIXME!! Make sure it is valid at all the call sites
 */
void ext4_discard_preallocations(struct inode *inode)
{
    struct ext4_inode_info *ei = EXT4_I(inode);
    struct super_block *sb = inode->i_sb;
    struct buffer_head *bitmap_bh = NULL;
    struct ext4_prealloc_space *pa, *tmp;
    ext4_group_t group = 0;
    struct list_head list;
    struct ext4_buddy e4b;
    int err;

    if (!S_ISREG(inode->i_mode)) {
        /*BUG_ON(!list_empty(&ei->i_prealloc_list));*/
        return;
    }

    mb_debug(1, "discard preallocation for inode %lu\n", inode->i_ino);
    trace_ext4_discard_preallocations(inode);

    INIT_LIST_HEAD(&list);

repeat:
    /* first, collect all pa's in the inode */
    spin_lock(&ei->i_prealloc_lock);
    while (!list_empty(&ei->i_prealloc_list)) {
        pa = list_entry(ei->i_prealloc_list.next,
                struct ext4_prealloc_space, pa_inode_list);
        BUG_ON(pa->pa_obj_lock != &ei->i_prealloc_lock);
        spin_lock(&pa->pa_lock);
        if (atomic_read(&pa->pa_count)) {
            /* this shouldn't happen often - nobody should
             * use preallocation while we're discarding it */
            spin_unlock(&pa->pa_lock);
            spin_unlock(&ei->i_prealloc_lock);
            ext4_msg(sb, KERN_ERR,
                 "uh-oh! used pa while discarding");
            WARN_ON(1);
            schedule_timeout_uninterruptible(HZ);
            goto repeat;

        }
        if (pa->pa_deleted == 0) {
            pa->pa_deleted = 1;
            spin_unlock(&pa->pa_lock);
            list_del_rcu(&pa->pa_inode_list);
            list_add(&pa->u.pa_tmp_list, &list);
            continue;
        }

        /* someone is deleting pa right now */
        spin_unlock(&pa->pa_lock);
        spin_unlock(&ei->i_prealloc_lock);

        /* we have to wait here because pa_deleted
         * doesn't mean pa is already unlinked from
         * the list. as we might be called from
         * ->clear_inode() the inode will get freed
         * and concurrent thread which is unlinking
         * pa from inode's list may access already
         * freed memory, bad-bad-bad */

        /* XXX: if this happens too often, we can
         * add a flag to force wait only in case
         * of ->clear_inode(), but not in case of
         * regular truncate */
        schedule_timeout_uninterruptible(HZ);
        goto repeat;
    }
    spin_unlock(&ei->i_prealloc_lock);

    list_for_each_entry_safe(pa, tmp, &list, u.pa_tmp_list) {
        BUG_ON(pa->pa_type != MB_INODE_PA);
        ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, NULL);

        err = ext4_mb_load_buddy(sb, group, &e4b);
        if (err) {
            ext4_error(sb, "Error loading buddy information for %u",
                    group);
            continue;
        }

        bitmap_bh = ext4_read_block_bitmap(sb, group);
        if (bitmap_bh == NULL) {
            ext4_error(sb, "Error reading block bitmap for %u",
                    group);
            ext4_mb_unload_buddy(&e4b);
            continue;
        }

        ext4_lock_group(sb, group);
        list_del(&pa->pa_group_list);
        ext4_mb_release_inode_pa(&e4b, bitmap_bh, pa);
        ext4_unlock_group(sb, group);

        ext4_mb_unload_buddy(&e4b);
        put_bh(bitmap_bh);

        list_del(&pa->u.pa_tmp_list);
        call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
    }
}

#ifdef CONFIG_EXT4_DEBUG
static void ext4_mb_show_ac(struct ext4_allocation_context *ac)
{
    struct super_block *sb = ac->ac_sb;
    ext4_group_t ngroups, i;

    if (!mb_enable_debug ||
        (EXT4_SB(sb)->s_mount_flags & EXT4_MF_FS_ABORTED))
        return;

    ext4_msg(ac->ac_sb, KERN_ERR, "Can't allocate:"
            " Allocation context details:");
    ext4_msg(ac->ac_sb, KERN_ERR, "status %d flags %d",
            ac->ac_status, ac->ac_flags);
    ext4_msg(ac->ac_sb, KERN_ERR, "orig %lu/%lu/%lu@%lu, "
            "goal %lu/%lu/%lu@%lu, "
            "best %lu/%lu/%lu@%lu cr %d",
            (unsigned long)ac->ac_o_ex.fe_group,
            (unsigned long)ac->ac_o_ex.fe_start,
            (unsigned long)ac->ac_o_ex.fe_len,
            (unsigned long)ac->ac_o_ex.fe_logical,
            (unsigned long)ac->ac_g_ex.fe_group,
            (unsigned long)ac->ac_g_ex.fe_start,
            (unsigned long)ac->ac_g_ex.fe_len,
            (unsigned long)ac->ac_g_ex.fe_logical,
            (unsigned long)ac->ac_b_ex.fe_group,
            (unsigned long)ac->ac_b_ex.fe_start,
            (unsigned long)ac->ac_b_ex.fe_len,
            (unsigned long)ac->ac_b_ex.fe_logical,
            (int)ac->ac_criteria);
    ext4_msg(ac->ac_sb, KERN_ERR, "%lu scanned, %d found",
         ac->ac_ex_scanned, ac->ac_found);
    ext4_msg(ac->ac_sb, KERN_ERR, "groups: ");
    ngroups = ext4_get_groups_count(sb);
    for (i = 0; i < ngroups; i++) {
        struct ext4_group_info *grp = ext4_get_group_info(sb, i);
        struct ext4_prealloc_space *pa;
        ext4_grpblk_t start;
        struct list_head *cur;
        ext4_lock_group(sb, i);
        list_for_each(cur, &grp->bb_prealloc_list) {
            pa = list_entry(cur, struct ext4_prealloc_space,
                    pa_group_list);
            spin_lock(&pa->pa_lock);
            ext4_get_group_no_and_offset(sb, pa->pa_pstart,
                             NULL, &start);
            spin_unlock(&pa->pa_lock);
            printk(KERN_ERR "PA:%u:%d:%u \n", i,
                   start, pa->pa_len);
        }
        ext4_unlock_group(sb, i);

        if (grp->bb_free == 0)
            continue;
        printk(KERN_ERR "%u: %d/%d \n",
               i, grp->bb_free, grp->bb_fragments);
    }
    printk(KERN_ERR "\n");
}
#else
static inline void ext4_mb_show_ac(struct ext4_allocation_context *ac)
{
    return;
}
#endif

/*
 * We use locality group preallocation for small size file. The size of the
 * file is determined by the current size or the resulting size after
 * allocation which ever is larger
 *
 * One can tune this size via /sys/fs/ext4/<partition>/mb_stream_req
 */
static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
{
    struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
    int bsbits = ac->ac_sb->s_blocksize_bits;
    loff_t size, isize;

    if (!(ac->ac_flags & EXT4_MB_HINT_DATA))
        return;

    if (unlikely(ac->ac_flags & EXT4_MB_HINT_GOAL_ONLY))
        return;

    size = ac->ac_o_ex.fe_logical + EXT4_C2B(sbi, ac->ac_o_ex.fe_len);
    isize = (i_size_read(ac->ac_inode) + ac->ac_sb->s_blocksize - 1)
        >> bsbits;

    if ((size == isize) &&
        !ext4_fs_is_busy(sbi) &&
        (atomic_read(&ac->ac_inode->i_writecount) == 0)) {
        ac->ac_flags |= EXT4_MB_HINT_NOPREALLOC;
        return;
    }

    if (sbi->s_mb_group_prealloc <= 0) {
        ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
        return;
    }

    /* don't use group allocation for large files */
    size = max(size, isize);
    if (size > sbi->s_mb_stream_request) {
        ac->ac_flags |= EXT4_MB_STREAM_ALLOC;
        return;
    }

    BUG_ON(ac->ac_lg != NULL);
    /*
     * locality group prealloc space are per cpu. The reason for having
     * per cpu locality group is to reduce the contention between block
     * request from multiple CPUs.
     */
    ac->ac_lg = __this_cpu_ptr(sbi->s_locality_groups);

    /* we're going to use group allocation */
    ac->ac_flags |= EXT4_MB_HINT_GROUP_ALLOC;

    /* serialize all allocations in the group */
    mutex_lock(&ac->ac_lg->lg_mutex);
}

static noinline_for_stack int
ext4_mb_initialize_context(struct ext4_allocation_context *ac,
                struct ext4_allocation_request *ar)
{
    struct super_block *sb = ar->inode->i_sb;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    struct ext4_super_block *es = sbi->s_es;
    ext4_group_t group;
    unsigned int len;
    ext4_fsblk_t goal;
    ext4_grpblk_t block;

    /* we can't allocate > group size */
    len = ar->len;

    /* just a dirty hack to filter too big requests  */
    if (len >= EXT4_CLUSTERS_PER_GROUP(sb) - 10)
        len = EXT4_CLUSTERS_PER_GROUP(sb) - 10;

    /* start searching from the goal */
    goal = ar->goal;
    if (goal < le32_to_cpu(es->s_first_data_block) ||
            goal >= ext4_blocks_count(es))
        goal = le32_to_cpu(es->s_first_data_block);
    ext4_get_group_no_and_offset(sb, goal, &group, &block);

    /* set up allocation goals */
    ac->ac_b_ex.fe_logical = ar->logical & ~(sbi->s_cluster_ratio - 1);
    ac->ac_status = AC_STATUS_CONTINUE;
    ac->ac_sb = sb;
    ac->ac_inode = ar->inode;
    ac->ac_o_ex.fe_logical = ac->ac_b_ex.fe_logical;
    ac->ac_o_ex.fe_group = group;
    ac->ac_o_ex.fe_start = block;
    ac->ac_o_ex.fe_len = len;
    ac->ac_g_ex = ac->ac_o_ex;
    ac->ac_flags = ar->flags;

    /* we have to define context: we'll we work with a file or
     * locality group. this is a policy, actually */
    ext4_mb_group_or_file(ac);

    mb_debug(1, "init ac: %u blocks @ %u, goal %u, flags %x, 2^%d, "
            "left: %u/%u, right %u/%u to %swritable\n",
            (unsigned) ar->len, (unsigned) ar->logical,
            (unsigned) ar->goal, ac->ac_flags, ac->ac_2order,
            (unsigned) ar->lleft, (unsigned) ar->pleft,
            (unsigned) ar->lright, (unsigned) ar->pright,
            atomic_read(&ar->inode->i_writecount) ? "" : "non-");
    return 0;

}

static noinline_for_stack void
ext4_mb_discard_lg_preallocations(struct super_block *sb,
                    struct ext4_locality_group *lg,
                    int order, int total_entries)
{
    ext4_group_t group = 0;
    struct ext4_buddy e4b;
    struct list_head discard_list;
    struct ext4_prealloc_space *pa, *tmp;

    mb_debug(1, "discard locality group preallocation\n");

    INIT_LIST_HEAD(&discard_list);

    spin_lock(&lg->lg_prealloc_lock);
    list_for_each_entry_rcu(pa, &lg->lg_prealloc_list[order],
                        pa_inode_list) {
        spin_lock(&pa->pa_lock);
        if (atomic_read(&pa->pa_count)) {
            /*
             * This is the pa that we just used
             * for block allocation. So don't
             * free that
             */
            spin_unlock(&pa->pa_lock);
            continue;
        }
        if (pa->pa_deleted) {
            spin_unlock(&pa->pa_lock);
            continue;
        }
        /* only lg prealloc space */
        BUG_ON(pa->pa_type != MB_GROUP_PA);

        /* seems this one can be freed ... */
        pa->pa_deleted = 1;
        spin_unlock(&pa->pa_lock);

        list_del_rcu(&pa->pa_inode_list);
        list_add(&pa->u.pa_tmp_list, &discard_list);

        total_entries--;
        if (total_entries <= 5) {
            /*
             * we want to keep only 5 entries
             * allowing it to grow to 8. This
             * mak sure we don't call discard
             * soon for this list.
             */
            break;
        }
    }
    spin_unlock(&lg->lg_prealloc_lock);

    list_for_each_entry_safe(pa, tmp, &discard_list, u.pa_tmp_list) {

        ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, NULL);
        if (ext4_mb_load_buddy(sb, group, &e4b)) {
            ext4_error(sb, "Error loading buddy information for %u",
                    group);
            continue;
        }
        ext4_lock_group(sb, group);
        list_del(&pa->pa_group_list);
        ext4_mb_release_group_pa(&e4b, pa);
        ext4_unlock_group(sb, group);

        ext4_mb_unload_buddy(&e4b);
        list_del(&pa->u.pa_tmp_list);
        call_rcu(&(pa)->u.pa_rcu, ext4_mb_pa_callback);
    }
}

/*
 * We have incremented pa_count. So it cannot be freed at this
 * point. Also we hold lg_mutex. So no parallel allocation is
 * possible from this lg. That means pa_free cannot be updated.
 *
 * A parallel ext4_mb_discard_group_preallocations is possible.
 * which can cause the lg_prealloc_list to be updated.
 */

static void ext4_mb_add_n_trim(struct ext4_allocation_context *ac)
{
    int order, added = 0, lg_prealloc_count = 1;
    struct super_block *sb = ac->ac_sb;
    struct ext4_locality_group *lg = ac->ac_lg;
    struct ext4_prealloc_space *tmp_pa, *pa = ac->ac_pa;

    order = fls(pa->pa_free) - 1;
    if (order > PREALLOC_TB_SIZE - 1)
        /* The max size of hash table is PREALLOC_TB_SIZE */
        order = PREALLOC_TB_SIZE - 1;
    /* Add the prealloc space to lg */
    rcu_read_lock();
    list_for_each_entry_rcu(tmp_pa, &lg->lg_prealloc_list[order],
                        pa_inode_list) {
        spin_lock(&tmp_pa->pa_lock);
        if (tmp_pa->pa_deleted) {
            spin_unlock(&tmp_pa->pa_lock);
            continue;
        }
        if (!added && pa->pa_free < tmp_pa->pa_free) {
            /* Add to the tail of the previous entry */
            list_add_tail_rcu(&pa->pa_inode_list,
                        &tmp_pa->pa_inode_list);
            added = 1;
            /*
             * we want to count the total
             * number of entries in the list
             */
        }
        spin_unlock(&tmp_pa->pa_lock);
        lg_prealloc_count++;
    }
    if (!added)
        list_add_tail_rcu(&pa->pa_inode_list,
                    &lg->lg_prealloc_list[order]);
    rcu_read_unlock();

    /* Now trim the list to be not more than 8 elements */
    if (lg_prealloc_count > 8) {
        ext4_mb_discard_lg_preallocations(sb, lg,
                        order, lg_prealloc_count);
        return;
    }
    return ;
}

/*
 * release all resource we used in allocation
 */
static int ext4_mb_release_context(struct ext4_allocation_context *ac)
{
    struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
    struct ext4_prealloc_space *pa = ac->ac_pa;
    if (pa) {
        if (pa->pa_type == MB_GROUP_PA) {
            /* see comment in ext4_mb_use_group_pa() */
            spin_lock(&pa->pa_lock);
            pa->pa_pstart += EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
            pa->pa_lstart += EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
            pa->pa_free -= ac->ac_b_ex.fe_len;
            pa->pa_len -= ac->ac_b_ex.fe_len;
            spin_unlock(&pa->pa_lock);
        }
    }
    if (pa) {
        /*
         * We want to add the pa to the right bucket.
         * Remove it from the list and while adding
         * make sure the list to which we are adding
         * doesn't grow big.
         */
        if ((pa->pa_type == MB_GROUP_PA) && likely(pa->pa_free)) {
            spin_lock(pa->pa_obj_lock);
            list_del_rcu(&pa->pa_inode_list);
            spin_unlock(pa->pa_obj_lock);
            ext4_mb_add_n_trim(ac);
        }
        ext4_mb_put_pa(ac, ac->ac_sb, pa);
    }
    if (ac->ac_bitmap_page)
        page_cache_release(ac->ac_bitmap_page);
    if (ac->ac_buddy_page)
        page_cache_release(ac->ac_buddy_page);
    if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
        mutex_unlock(&ac->ac_lg->lg_mutex);
    ext4_mb_collect_stats(ac);
    return 0;
}

static int ext4_mb_discard_preallocations(struct super_block *sb, int needed)
{
    ext4_group_t i, ngroups = ext4_get_groups_count(sb);
    int ret;
    int freed = 0;

    trace_ext4_mb_discard_preallocations(sb, needed);
    for (i = 0; i < ngroups && needed > 0; i++) {
        ret = ext4_mb_discard_group_preallocations(sb, i, needed);
        freed += ret;
        needed -= ret;
    }

    return freed;
}

/*
 * Main entry point into mballoc to allocate blocks
 * it tries to use preallocation first, then falls back
 * to usual allocation
 */
ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
                struct ext4_allocation_request *ar, int *errp)
{
    int freed;
    struct ext4_allocation_context *ac = NULL;
    struct ext4_sb_info *sbi;
    struct super_block *sb;
    ext4_fsblk_t block = 0;
    unsigned int inquota = 0;
    unsigned int reserv_clstrs = 0;

    sb = ar->inode->i_sb;
    sbi = EXT4_SB(sb);

    trace_ext4_request_blocks(ar);

    /* Allow to use superuser reservation for quota file */
    if (IS_NOQUOTA(ar->inode))
        ar->flags |= EXT4_MB_USE_ROOT_BLOCKS;

    /*
     * For delayed allocation, we could skip the ENOSPC and
     * EDQUOT check, as blocks and quotas have been already
     * reserved when data being copied into pagecache.
     */
    if (ext4_test_inode_state(ar->inode, EXT4_STATE_DELALLOC_RESERVED))
        ar->flags |= EXT4_MB_DELALLOC_RESERVED;
    else {
        /* Without delayed allocation we need to verify
         * there is enough free blocks to do block allocation
         * and verify allocation doesn't exceed the quota limits.
         */
        while (ar->len &&
            ext4_claim_free_clusters(sbi, ar->len, ar->flags)) {

            /* let others to free the space */
            yield();
            ar->len = ar->len >> 1;
        }
        if (!ar->len) {
            *errp = -ENOSPC;
            return 0;
        }
        reserv_clstrs = ar->len;
        if (ar->flags & EXT4_MB_USE_ROOT_BLOCKS) {
            dquot_alloc_block_nofail(ar->inode,
                         EXT4_C2B(sbi, ar->len));
        } else {
            while (ar->len &&
                dquot_alloc_block(ar->inode,
                          EXT4_C2B(sbi, ar->len))) {

                ar->flags |= EXT4_MB_HINT_NOPREALLOC;
                ar->len--;
            }
        }
        inquota = ar->len;
        if (ar->len == 0) {
            *errp = -EDQUOT;
            goto out;
        }
    }

    ac = kmem_cache_zalloc(ext4_ac_cachep, GFP_NOFS);
    if (!ac) {
        ar->len = 0;
        *errp = -ENOMEM;
        goto out;
    }

    *errp = ext4_mb_initialize_context(ac, ar);
    if (*errp) {
        ar->len = 0;
        goto out;
    }

    ac->ac_op = EXT4_MB_HISTORY_PREALLOC;
    if (!ext4_mb_use_preallocated(ac)) {
        ac->ac_op = EXT4_MB_HISTORY_ALLOC;
        ext4_mb_normalize_request(ac, ar);
repeat:
        /* allocate space in core */
        *errp = ext4_mb_regular_allocator(ac);
        if (*errp)
            goto errout;

        /* as we've just preallocated more space than
         * user requested orinally, we store allocated
         * space in a special descriptor */
        if (ac->ac_status == AC_STATUS_FOUND &&
                ac->ac_o_ex.fe_len < ac->ac_b_ex.fe_len)
            ext4_mb_new_preallocation(ac);
    }
    if (likely(ac->ac_status == AC_STATUS_FOUND)) {
        *errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs);
        if (*errp == -EAGAIN) {
            /*
             * drop the reference that we took
             * in ext4_mb_use_best_found
             */
            ext4_mb_release_context(ac);
            ac->ac_b_ex.fe_group = 0;
            ac->ac_b_ex.fe_start = 0;
            ac->ac_b_ex.fe_len = 0;
            ac->ac_status = AC_STATUS_CONTINUE;
            goto repeat;
        } else if (*errp)
        errout:
            ext4_discard_allocated_blocks(ac);
        else {
            block = ext4_grp_offs_to_block(sb, &ac->ac_b_ex);
            ar->len = ac->ac_b_ex.fe_len;
        }
    } else {
        freed  = ext4_mb_discard_preallocations(sb, ac->ac_o_ex.fe_len);
        if (freed)
            goto repeat;
        *errp = -ENOSPC;
    }

    if (*errp) {
        ac->ac_b_ex.fe_len = 0;
        ar->len = 0;
        ext4_mb_show_ac(ac);
    }
    ext4_mb_release_context(ac);
out:
    if (ac)
        kmem_cache_free(ext4_ac_cachep, ac);
    if (inquota && ar->len < inquota)
        dquot_free_block(ar->inode, EXT4_C2B(sbi, inquota - ar->len));
    if (!ar->len) {
        if (!ext4_test_inode_state(ar->inode,
                       EXT4_STATE_DELALLOC_RESERVED))
            /* release all the reserved blocks if non delalloc */
            percpu_counter_sub(&sbi->s_dirtyclusters_counter,
                        reserv_clstrs);
    }

    trace_ext4_allocate_blocks(ar, (unsigned long long)block);

    return block;
}

/*
 * We can merge two free data extents only if the physical blocks
 * are contiguous, AND the extents were freed by the same transaction,
 * AND the blocks are associated with the same group.
 */
static int can_merge(struct ext4_free_data *entry1,
            struct ext4_free_data *entry2)
{
    if ((entry1->efd_tid == entry2->efd_tid) &&
        (entry1->efd_group == entry2->efd_group) &&
        ((entry1->efd_start_cluster + entry1->efd_count) == entry2->efd_start_cluster))
        return 1;
    return 0;
}

static noinline_for_stack int
ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
              struct ext4_free_data *new_entry)
{
    ext4_group_t group = e4b->bd_group;
    ext4_grpblk_t cluster;
    struct ext4_free_data *entry;
    struct ext4_group_info *db = e4b->bd_info;
    struct super_block *sb = e4b->bd_sb;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    struct rb_node **n = &db->bb_free_root.rb_node, *node;
    struct rb_node *parent = NULL, *new_node;

    BUG_ON(!ext4_handle_valid(handle));
    BUG_ON(e4b->bd_bitmap_page == NULL);
    BUG_ON(e4b->bd_buddy_page == NULL);

    new_node = &new_entry->efd_node;
    cluster = new_entry->efd_start_cluster;

    if (!*n) {
        /* first free block exent. We need to
           protect buddy cache from being freed,
         * otherwise we'll refresh it from
         * on-disk bitmap and lose not-yet-available
         * blocks */
        page_cache_get(e4b->bd_buddy_page);
        page_cache_get(e4b->bd_bitmap_page);
    }
    while (*n) {
        parent = *n;
        entry = rb_entry(parent, struct ext4_free_data, efd_node);
        if (cluster < entry->efd_start_cluster)
            n = &(*n)->rb_left;
        else if (cluster >= (entry->efd_start_cluster + entry->efd_count))
            n = &(*n)->rb_right;
        else {
            ext4_grp_locked_error(sb, group, 0,
                ext4_group_first_block_no(sb, group) +
                EXT4_C2B(sbi, cluster),
                "Block already on to-be-freed list");
            return 0;
        }
    }

    rb_link_node(new_node, parent, n);
    rb_insert_color(new_node, &db->bb_free_root);

    /* Now try to see the extent can be merged to left and right */
    node = rb_prev(new_node);
    if (node) {
        entry = rb_entry(node, struct ext4_free_data, efd_node);
        if (can_merge(entry, new_entry)) {
            new_entry->efd_start_cluster = entry->efd_start_cluster;
            new_entry->efd_count += entry->efd_count;
            rb_erase(node, &(db->bb_free_root));
            ext4_journal_callback_del(handle, &entry->efd_jce);
            kmem_cache_free(ext4_free_data_cachep, entry);
        }
    }

    node = rb_next(new_node);
    if (node) {
        entry = rb_entry(node, struct ext4_free_data, efd_node);
        if (can_merge(new_entry, entry)) {
            new_entry->efd_count += entry->efd_count;
            rb_erase(node, &(db->bb_free_root));
            ext4_journal_callback_del(handle, &entry->efd_jce);
            kmem_cache_free(ext4_free_data_cachep, entry);
        }
    }
    /* Add the extent to transaction's private list */
    ext4_journal_callback_add(handle, ext4_free_data_callback,
                  &new_entry->efd_jce);
    return 0;
}

void ext4_free_blocks(handle_t *handle, struct inode *inode,
              struct buffer_head *bh, ext4_fsblk_t block,
              unsigned long count, int flags)
{
    struct buffer_head *bitmap_bh = NULL;
    struct super_block *sb = inode->i_sb;
    struct ext4_group_desc *gdp;
    unsigned long freed = 0;
    unsigned int overflow;
    ext4_grpblk_t bit;
    struct buffer_head *gd_bh;
    ext4_group_t block_group;
    struct ext4_sb_info *sbi;
    struct ext4_buddy e4b;
    unsigned int count_clusters;
    int err = 0;
    int ret;

    if (bh) {
        if (block)
            BUG_ON(block != bh->b_blocknr);
        else
            block = bh->b_blocknr;
    }

    sbi = EXT4_SB(sb);
    if (!(flags & EXT4_FREE_BLOCKS_VALIDATED) &&
        !ext4_data_block_valid(sbi, block, count)) {
        ext4_error(sb, "Freeing blocks not in datazone - "
               "block = %llu, count = %lu", block, count);
        goto error_return;
    }

    ext4_debug("freeing block %llu\n", block);
    trace_ext4_free_blocks(inode, block, count, flags);

    if (flags & EXT4_FREE_BLOCKS_FORGET) {
        struct buffer_head *tbh = bh;
        int i;

        BUG_ON(bh && (count > 1));

        for (i = 0; i < count; i++) {
            if (!bh)
                tbh = sb_find_get_block(inode->i_sb,
                            block + i);
            if (unlikely(!tbh))
                continue;
            ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
                    inode, tbh, block + i);
        }
    }

    /*
     * We need to make sure we don't reuse the freed block until
     * after the transaction is committed, which we can do by
     * treating the block as metadata, below.  We make an
     * exception if the inode is to be written in writeback mode
     * since writeback mode has weak data consistency guarantees.
     */
    if (!ext4_should_writeback_data(inode))
        flags |= EXT4_FREE_BLOCKS_METADATA;

    /*
     * If the extent to be freed does not begin on a cluster
     * boundary, we need to deal with partial clusters at the
     * beginning and end of the extent.  Normally we will free
     * blocks at the beginning or the end unless we are explicitly
     * requested to avoid doing so.
     */
    overflow = block & (sbi->s_cluster_ratio - 1);
    if (overflow) {
        if (flags & EXT4_FREE_BLOCKS_NOFREE_FIRST_CLUSTER) {
            overflow = sbi->s_cluster_ratio - overflow;
            block += overflow;
            if (count > overflow)
                count -= overflow;
            else
                return;
        } else {
            block -= overflow;
            count += overflow;
        }
    }
    overflow = count & (sbi->s_cluster_ratio - 1);
    if (overflow) {
        if (flags & EXT4_FREE_BLOCKS_NOFREE_LAST_CLUSTER) {
            if (count > overflow)
                count -= overflow;
            else
                return;
        } else
            count += sbi->s_cluster_ratio - overflow;
    }

do_more:
    overflow = 0;
    ext4_get_group_no_and_offset(sb, block, &block_group, &bit);

    /*
     * Check to see if we are freeing blocks across a group
     * boundary.
     */
    if (EXT4_C2B(sbi, bit) + count > EXT4_BLOCKS_PER_GROUP(sb)) {
        overflow = EXT4_C2B(sbi, bit) + count -
            EXT4_BLOCKS_PER_GROUP(sb);
        count -= overflow;
    }
    count_clusters = EXT4_B2C(sbi, count);
    bitmap_bh = ext4_read_block_bitmap(sb, block_group);
    if (!bitmap_bh) {
        err = -EIO;
        goto error_return;
    }
    gdp = ext4_get_group_desc(sb, block_group, &gd_bh);
    if (!gdp) {
        err = -EIO;
        goto error_return;
    }

    if (in_range(ext4_block_bitmap(sb, gdp), block, count) ||
        in_range(ext4_inode_bitmap(sb, gdp), block, count) ||
        in_range(block, ext4_inode_table(sb, gdp),
             EXT4_SB(sb)->s_itb_per_group) ||
        in_range(block + count - 1, ext4_inode_table(sb, gdp),
             EXT4_SB(sb)->s_itb_per_group)) {

        ext4_error(sb, "Freeing blocks in system zone - "
               "Block = %llu, count = %lu", block, count);
        /* err = 0. ext4_std_error should be a no op */
        goto error_return;
    }

    BUFFER_TRACE(bitmap_bh, "getting write access");
    err = ext4_journal_get_write_access(handle, bitmap_bh);
    if (err)
        goto error_return;

    /*
     * We are about to modify some metadata.  Call the journal APIs
     * to unshare ->b_data if a currently-committing transaction is
     * using it
     */
    BUFFER_TRACE(gd_bh, "get_write_access");
    err = ext4_journal_get_write_access(handle, gd_bh);
    if (err)
        goto error_return;
#ifdef AGGRESSIVE_CHECK
    {
        int i;
        for (i = 0; i < count_clusters; i++)
            BUG_ON(!mb_test_bit(bit + i, bitmap_bh->b_data));
    }
#endif
    trace_ext4_mballoc_free(sb, inode, block_group, bit, count_clusters);

    err = ext4_mb_load_buddy(sb, block_group, &e4b);
    if (err)
        goto error_return;

    if ((flags & EXT4_FREE_BLOCKS_METADATA) && ext4_handle_valid(handle)) {
        struct ext4_free_data *new_entry;
        /*
         * blocks being freed are metadata. these blocks shouldn't
         * be used until this transaction is committed
         */
        new_entry = kmem_cache_alloc(ext4_free_data_cachep, GFP_NOFS);
        if (!new_entry) {
            ext4_mb_unload_buddy(&e4b);
            err = -ENOMEM;
            goto error_return;
        }
        new_entry->efd_start_cluster = bit;
        new_entry->efd_group = block_group;
        new_entry->efd_count = count_clusters;
        new_entry->efd_tid = handle->h_transaction->t_tid;

        ext4_lock_group(sb, block_group);
        mb_clear_bits(bitmap_bh->b_data, bit, count_clusters);
        ext4_mb_free_metadata(handle, &e4b, new_entry);
    } else {
        /* need to update group_info->bb_free and bitmap
         * with group lock held. generate_buddy look at
         * them with group lock_held
         */
        if (test_opt(sb, DISCARD))
            ext4_issue_discard(sb, block_group, bit, count);
        ext4_lock_group(sb, block_group);
        mb_clear_bits(bitmap_bh->b_data, bit, count_clusters);
        mb_free_blocks(inode, &e4b, bit, count_clusters);
    }

    ret = ext4_free_group_clusters(sb, gdp) + count_clusters;
    ext4_free_group_clusters_set(sb, gdp, ret);
    ext4_block_bitmap_csum_set(sb, block_group, gdp, bitmap_bh);
    ext4_group_desc_csum_set(sb, block_group, gdp);
    ext4_unlock_group(sb, block_group);
    percpu_counter_add(&sbi->s_freeclusters_counter, count_clusters);

    if (sbi->s_log_groups_per_flex) {
        ext4_group_t flex_group = ext4_flex_group(sbi, block_group);
        atomic_add(count_clusters,
               &sbi->s_flex_groups[flex_group].free_clusters);
    }

    ext4_mb_unload_buddy(&e4b);

    freed += count;

    if (!(flags & EXT4_FREE_BLOCKS_NO_QUOT_UPDATE))
        dquot_free_block(inode, EXT4_C2B(sbi, count_clusters));

    /* We dirtied the bitmap block */
    BUFFER_TRACE(bitmap_bh, "dirtied bitmap block");
    err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);

    /* And the group descriptor block */
    BUFFER_TRACE(gd_bh, "dirtied group descriptor block");
    ret = ext4_handle_dirty_metadata(handle, NULL, gd_bh);
    if (!err)
        err = ret;

    if (overflow && !err) {
        block += count;
        count = overflow;
        put_bh(bitmap_bh);
        goto do_more;
    }
error_return:
    brelse(bitmap_bh);
    ext4_std_error(sb, err);
    return;
}

int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
             ext4_fsblk_t block, unsigned long count)
{
    struct buffer_head *bitmap_bh = NULL;
    struct buffer_head *gd_bh;
    ext4_group_t block_group;
    ext4_grpblk_t bit;
    unsigned int i;
    struct ext4_group_desc *desc;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    struct ext4_buddy e4b;
    int err = 0, ret, blk_free_count;
    ext4_grpblk_t blocks_freed;

    ext4_debug("Adding block(s) %llu-%llu\n", block, block + count - 1);

    if (count == 0)
        return 0;

    ext4_get_group_no_and_offset(sb, block, &block_group, &bit);
    /*
     * Check to see if we are freeing blocks across a group
     * boundary.
     */
    if (bit + count > EXT4_BLOCKS_PER_GROUP(sb)) {
        ext4_warning(sb, "too much blocks added to group %u\n",
                 block_group);
        err = -EINVAL;
        goto error_return;
    }

    bitmap_bh = ext4_read_block_bitmap(sb, block_group);
    if (!bitmap_bh) {
        err = -EIO;
        goto error_return;
    }

    desc = ext4_get_group_desc(sb, block_group, &gd_bh);
    if (!desc) {
        err = -EIO;
        goto error_return;
    }

    if (in_range(ext4_block_bitmap(sb, desc), block, count) ||
        in_range(ext4_inode_bitmap(sb, desc), block, count) ||
        in_range(block, ext4_inode_table(sb, desc), sbi->s_itb_per_group) ||
        in_range(block + count - 1, ext4_inode_table(sb, desc),
             sbi->s_itb_per_group)) {
        ext4_error(sb, "Adding blocks in system zones - "
               "Block = %llu, count = %lu",
               block, count);
        err = -EINVAL;
        goto error_return;
    }

    BUFFER_TRACE(bitmap_bh, "getting write access");
    err = ext4_journal_get_write_access(handle, bitmap_bh);
    if (err)
        goto error_return;

    /*
     * We are about to modify some metadata.  Call the journal APIs
     * to unshare ->b_data if a currently-committing transaction is
     * using it
     */
    BUFFER_TRACE(gd_bh, "get_write_access");
    err = ext4_journal_get_write_access(handle, gd_bh);
    if (err)
        goto error_return;

    for (i = 0, blocks_freed = 0; i < count; i++) {
        BUFFER_TRACE(bitmap_bh, "clear bit");
        if (!mb_test_bit(bit + i, bitmap_bh->b_data)) {
            ext4_error(sb, "bit already cleared for block %llu",
                   (ext4_fsblk_t)(block + i));
            BUFFER_TRACE(bitmap_bh, "bit already cleared");
        } else {
            blocks_freed++;
        }
    }

    err = ext4_mb_load_buddy(sb, block_group, &e4b);
    if (err)
        goto error_return;

    /*
     * need to update group_info->bb_free and bitmap
     * with group lock held. generate_buddy look at
     * them with group lock_held
     */
    ext4_lock_group(sb, block_group);
    mb_clear_bits(bitmap_bh->b_data, bit, count);
    mb_free_blocks(NULL, &e4b, bit, count);
    blk_free_count = blocks_freed + ext4_free_group_clusters(sb, desc);
    ext4_free_group_clusters_set(sb, desc, blk_free_count);
    ext4_block_bitmap_csum_set(sb, block_group, desc, bitmap_bh);
    ext4_group_desc_csum_set(sb, block_group, desc);
    ext4_unlock_group(sb, block_group);
    percpu_counter_add(&sbi->s_freeclusters_counter,
               EXT4_B2C(sbi, blocks_freed));

    if (sbi->s_log_groups_per_flex) {
        ext4_group_t flex_group = ext4_flex_group(sbi, block_group);
        atomic_add(EXT4_B2C(sbi, blocks_freed),
               &sbi->s_flex_groups[flex_group].free_clusters);
    }

    ext4_mb_unload_buddy(&e4b);

    /* We dirtied the bitmap block */
    BUFFER_TRACE(bitmap_bh, "dirtied bitmap block");
    err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);

    /* And the group descriptor block */
    BUFFER_TRACE(gd_bh, "dirtied group descriptor block");
    ret = ext4_handle_dirty_metadata(handle, NULL, gd_bh);
    if (!err)
        err = ret;

error_return:
    brelse(bitmap_bh);
    ext4_std_error(sb, err);
    return err;
}

static void ext4_trim_extent(struct super_block *sb, int start, int count,
                 ext4_group_t group, struct ext4_buddy *e4b)
{
    struct ext4_free_extent ex;

    trace_ext4_trim_extent(sb, group, start, count);

    assert_spin_locked(ext4_group_lock_ptr(sb, group));

    ex.fe_start = start;
    ex.fe_group = group;
    ex.fe_len = count;

    /*
     * Mark blocks used, so no one can reuse them while
     * being trimmed.
     */
    mb_mark_used(e4b, &ex);
    ext4_unlock_group(sb, group);
    ext4_issue_discard(sb, group, start, count);
    ext4_lock_group(sb, group);
    mb_free_blocks(NULL, e4b, start, ex.fe_len);
}

static ext4_grpblk_t
ext4_trim_all_free(struct super_block *sb, ext4_group_t group,
           ext4_grpblk_t start, ext4_grpblk_t max,
           ext4_grpblk_t minblocks)
{
    void *bitmap;
    ext4_grpblk_t next, count = 0, free_count = 0;
    struct ext4_buddy e4b;
    int ret;

    trace_ext4_trim_all_free(sb, group, start, max);

    ret = ext4_mb_load_buddy(sb, group, &e4b);
    if (ret) {
        ext4_error(sb, "Error in loading buddy "
                "information for %u", group);
        return ret;
    }
    bitmap = e4b.bd_bitmap;

    ext4_lock_group(sb, group);
    if (EXT4_MB_GRP_WAS_TRIMMED(e4b.bd_info) &&
        minblocks >= atomic_read(&EXT4_SB(sb)->s_last_trim_minblks))
        goto out;

    start = (e4b.bd_info->bb_first_free > start) ?
        e4b.bd_info->bb_first_free : start;

    while (start <= max) {
        start = mb_find_next_zero_bit(bitmap, max + 1, start);
        if (start > max)
            break;
        next = mb_find_next_bit(bitmap, max + 1, start);

        if ((next - start) >= minblocks) {
            ext4_trim_extent(sb, start,
                     next - start, group, &e4b);
            count += next - start;
        }
        free_count += next - start;
        start = next + 1;

        if (fatal_signal_pending(current)) {
            count = -ERESTARTSYS;
            break;
        }

        if (need_resched()) {
            ext4_unlock_group(sb, group);
            cond_resched();
            ext4_lock_group(sb, group);
        }

        if ((e4b.bd_info->bb_free - free_count) < minblocks)
            break;
    }

    if (!ret)
        EXT4_MB_GRP_SET_TRIMMED(e4b.bd_info);
out:
    ext4_unlock_group(sb, group);
    ext4_mb_unload_buddy(&e4b);

    ext4_debug("trimmed %d blocks in the group %d\n",
        count, group);

    return count;
}

int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
{
    struct ext4_group_info *grp;
    ext4_group_t group, first_group, last_group;
    ext4_grpblk_t cnt = 0, first_cluster, last_cluster;
    uint64_t start, end, minlen, trimmed = 0;
    ext4_fsblk_t first_data_blk =
            le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
    ext4_fsblk_t max_blks = ext4_blocks_count(EXT4_SB(sb)->s_es);
    int ret = 0;

    start = range->start >> sb->s_blocksize_bits;
    end = start + (range->len >> sb->s_blocksize_bits) - 1;
    minlen = EXT4_NUM_B2C(EXT4_SB(sb),
                  range->minlen >> sb->s_blocksize_bits);

    if (minlen > EXT4_CLUSTERS_PER_GROUP(sb) ||
        start >= max_blks ||
        range->len < sb->s_blocksize)
        return -EINVAL;
    if (end >= max_blks)
        end = max_blks - 1;
    if (end <= first_data_blk)
        goto out;
    if (start < first_data_blk)
        start = first_data_blk;

    /* Determine first and last group to examine based on start and end */
    ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) start,
                     &first_group, &first_cluster);
    ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) end,
                     &last_group, &last_cluster);

    /* end now represents the last cluster to discard in this group */
    end = EXT4_CLUSTERS_PER_GROUP(sb) - 1;

    for (group = first_group; group <= last_group; group++) {
        grp = ext4_get_group_info(sb, group);
        /* We only do this if the grp has never been initialized */
        if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
            ret = ext4_mb_init_group(sb, group);
            if (ret)
                break;
        }

        /*
         * For all the groups except the last one, last cluster will
         * always be EXT4_CLUSTERS_PER_GROUP(sb)-1, so we only need to
         * change it for the last group, note that last_cluster is
         * already computed earlier by ext4_get_group_no_and_offset()
         */
        if (group == last_group)
            end = last_cluster;

        if (grp->bb_free >= minlen) {
            cnt = ext4_trim_all_free(sb, group, first_cluster,
                        end, minlen);
            if (cnt < 0) {
                ret = cnt;
                break;
            }
            trimmed += cnt;
        }

        /*
         * For every group except the first one, we are sure
         * that the first cluster to discard will be cluster #0.
         */
        first_cluster = 0;
    }

    if (!ret)
        atomic_set(&EXT4_SB(sb)->s_last_trim_minblks, minlen);

out:
    range->len = EXT4_C2B(EXT4_SB(sb), trimmed) << sb->s_blocksize_bits;
    return ret;
}