localalloc.c

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/* -*- mode: c; c-basic-offset: 8; -*-
 * vim: noexpandtab sw=8 ts=8 sts=0:
 *
 * localalloc.c
 *
 * Node local data allocation
 *
 * Copyright (C) 2002, 2004 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * 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
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/fs.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/highmem.h>
#include <linux/bitops.h>

#include <cluster/masklog.h>

#include "ocfs2.h"

#include "alloc.h"
#include "blockcheck.h"
#include "dlmglue.h"
#include "inode.h"
#include "journal.h"
#include "localalloc.h"
#include "suballoc.h"
#include "super.h"
#include "sysfile.h"
#include "ocfs2_trace.h"

#include "buffer_head_io.h"

#define OCFS2_LOCAL_ALLOC(dinode)   (&((dinode)->id2.i_lab))

static u32 ocfs2_local_alloc_count_bits(struct ocfs2_dinode *alloc);

static int ocfs2_local_alloc_find_clear_bits(struct ocfs2_super *osb,
                         struct ocfs2_dinode *alloc,
                         u32 *numbits,
                         struct ocfs2_alloc_reservation *resv);

static void ocfs2_clear_local_alloc(struct ocfs2_dinode *alloc);

static int ocfs2_sync_local_to_main(struct ocfs2_super *osb,
                    handle_t *handle,
                    struct ocfs2_dinode *alloc,
                    struct inode *main_bm_inode,
                    struct buffer_head *main_bm_bh);

static int ocfs2_local_alloc_reserve_for_window(struct ocfs2_super *osb,
                        struct ocfs2_alloc_context **ac,
                        struct inode **bitmap_inode,
                        struct buffer_head **bitmap_bh);

static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
                    handle_t *handle,
                    struct ocfs2_alloc_context *ac);

static int ocfs2_local_alloc_slide_window(struct ocfs2_super *osb,
                      struct inode *local_alloc_inode);

/*
 * ocfs2_la_default_mb() - determine a default size, in megabytes of
 * the local alloc.
 *
 * Generally, we'd like to pick as large a local alloc as
 * possible. Performance on large workloads tends to scale
 * proportionally to la size. In addition to that, the reservations
 * code functions more efficiently as it can reserve more windows for
 * write.
 *
 * Some things work against us when trying to choose a large local alloc:
 *
 * - We need to ensure our sizing is picked to leave enough space in
 *   group descriptors for other allocations (such as block groups,
 *   etc). Picking default sizes which are a multiple of 4 could help
 *   - block groups are allocated in 2mb and 4mb chunks.
 *
 * - Likewise, we don't want to starve other nodes of bits on small
 *   file systems. This can easily be taken care of by limiting our
 *   default to a reasonable size (256M) on larger cluster sizes.
 *
 * - Some file systems can't support very large sizes - 4k and 8k in
 *   particular are limited to less than 128 and 256 megabytes respectively.
 *
 * The following reference table shows group descriptor and local
 * alloc maximums at various cluster sizes (4k blocksize)
 *
 * csize: 4K    group: 126M la: 121M
 * csize: 8K    group: 252M la: 243M
 * csize: 16K   group: 504M la: 486M
 * csize: 32K   group: 1008M    la: 972M
 * csize: 64K   group: 2016M    la: 1944M
 * csize: 128K  group: 4032M    la: 3888M
 * csize: 256K  group: 8064M    la: 7776M
 * csize: 512K  group: 16128M   la: 15552M
 * csize: 1024K group: 32256M   la: 31104M
 */
#define OCFS2_LA_MAX_DEFAULT_MB 256
#define OCFS2_LA_OLD_DEFAULT    8
unsigned int ocfs2_la_default_mb(struct ocfs2_super *osb)
{
    unsigned int la_mb;
    unsigned int gd_mb;
    unsigned int la_max_mb;
    unsigned int megs_per_slot;
    struct super_block *sb = osb->sb;

    gd_mb = ocfs2_clusters_to_megabytes(osb->sb,
        8 * ocfs2_group_bitmap_size(sb, 0, osb->s_feature_incompat));

    /*
     * This takes care of files systems with very small group
     * descriptors - 512 byte blocksize at cluster sizes lower
     * than 16K and also 1k blocksize with 4k cluster size.
     */
    if ((sb->s_blocksize == 512 && osb->s_clustersize <= 8192)
        || (sb->s_blocksize == 1024 && osb->s_clustersize == 4096))
        return OCFS2_LA_OLD_DEFAULT;

    /*
     * Leave enough room for some block groups and make the final
     * value we work from a multiple of 4.
     */
    gd_mb -= 16;
    gd_mb &= 0xFFFFFFFB;

    la_mb = gd_mb;

    /*
     * Keep window sizes down to a reasonable default
     */
    if (la_mb > OCFS2_LA_MAX_DEFAULT_MB) {
        /*
         * Some clustersize / blocksize combinations will have
         * given us a larger than OCFS2_LA_MAX_DEFAULT_MB
         * default size, but get poor distribution when
         * limited to exactly 256 megabytes.
         *
         * As an example, 16K clustersize at 4K blocksize
         * gives us a cluster group size of 504M. Paring the
         * local alloc size down to 256 however, would give us
         * only one window and around 200MB left in the
         * cluster group. Instead, find the first size below
         * 256 which would give us an even distribution.
         *
         * Larger cluster group sizes actually work out pretty
         * well when pared to 256, so we don't have to do this
         * for any group that fits more than two
         * OCFS2_LA_MAX_DEFAULT_MB windows.
         */
        if (gd_mb > (2 * OCFS2_LA_MAX_DEFAULT_MB))
            la_mb = 256;
        else {
            unsigned int gd_mult = gd_mb;

            while (gd_mult > 256)
                gd_mult = gd_mult >> 1;

            la_mb = gd_mult;
        }
    }

    megs_per_slot = osb->osb_clusters_at_boot / osb->max_slots;
    megs_per_slot = ocfs2_clusters_to_megabytes(osb->sb, megs_per_slot);
    /* Too many nodes, too few disk clusters. */
    if (megs_per_slot < la_mb)
        la_mb = megs_per_slot;

    /* We can't store more bits than we can in a block. */
    la_max_mb = ocfs2_clusters_to_megabytes(osb->sb,
                        ocfs2_local_alloc_size(sb) * 8);
    if (la_mb > la_max_mb)
        la_mb = la_max_mb;

    return la_mb;
}

void ocfs2_la_set_sizes(struct ocfs2_super *osb, int requested_mb)
{
    struct super_block *sb = osb->sb;
    unsigned int la_default_mb = ocfs2_la_default_mb(osb);
    unsigned int la_max_mb;

    la_max_mb = ocfs2_clusters_to_megabytes(sb,
                        ocfs2_local_alloc_size(sb) * 8);

    trace_ocfs2_la_set_sizes(requested_mb, la_max_mb, la_default_mb);

    if (requested_mb == -1) {
        /* No user request - use defaults */
        osb->local_alloc_default_bits =
            ocfs2_megabytes_to_clusters(sb, la_default_mb);
    } else if (requested_mb > la_max_mb) {
        /* Request is too big, we give the maximum available */
        osb->local_alloc_default_bits =
            ocfs2_megabytes_to_clusters(sb, la_max_mb);
    } else {
        osb->local_alloc_default_bits =
            ocfs2_megabytes_to_clusters(sb, requested_mb);
    }

    osb->local_alloc_bits = osb->local_alloc_default_bits;
}

static inline int ocfs2_la_state_enabled(struct ocfs2_super *osb)
{
    return (osb->local_alloc_state == OCFS2_LA_THROTTLED ||
        osb->local_alloc_state == OCFS2_LA_ENABLED);
}

void ocfs2_local_alloc_seen_free_bits(struct ocfs2_super *osb,
                      unsigned int num_clusters)
{
    spin_lock(&osb->osb_lock);
    if (osb->local_alloc_state == OCFS2_LA_DISABLED ||
        osb->local_alloc_state == OCFS2_LA_THROTTLED)
        if (num_clusters >= osb->local_alloc_default_bits) {
            cancel_delayed_work(&osb->la_enable_wq);
            osb->local_alloc_state = OCFS2_LA_ENABLED;
        }
    spin_unlock(&osb->osb_lock);
}

void ocfs2_la_enable_worker(struct work_struct *work)
{
    struct ocfs2_super *osb =
        container_of(work, struct ocfs2_super,
                 la_enable_wq.work);
    spin_lock(&osb->osb_lock);
    osb->local_alloc_state = OCFS2_LA_ENABLED;
    spin_unlock(&osb->osb_lock);
}

/*
 * Tell us whether a given allocation should use the local alloc
 * file. Otherwise, it has to go to the main bitmap.
 *
 * This function does semi-dirty reads of local alloc size and state!
 * This is ok however, as the values are re-checked once under mutex.
 */
int ocfs2_alloc_should_use_local(struct ocfs2_super *osb, u64 bits)
{
    int ret = 0;
    int la_bits;

    spin_lock(&osb->osb_lock);
    la_bits = osb->local_alloc_bits;

    if (!ocfs2_la_state_enabled(osb))
        goto bail;

    /* la_bits should be at least twice the size (in clusters) of
     * a new block group. We want to be sure block group
     * allocations go through the local alloc, so allow an
     * allocation to take up to half the bitmap. */
    if (bits > (la_bits / 2))
        goto bail;

    ret = 1;
bail:
    trace_ocfs2_alloc_should_use_local(
         (unsigned long long)bits, osb->local_alloc_state, la_bits, ret);
    spin_unlock(&osb->osb_lock);
    return ret;
}

int ocfs2_load_local_alloc(struct ocfs2_super *osb)
{
    int status = 0;
    struct ocfs2_dinode *alloc = NULL;
    struct buffer_head *alloc_bh = NULL;
    u32 num_used;
    struct inode *inode = NULL;
    struct ocfs2_local_alloc *la;

    if (osb->local_alloc_bits == 0)
        goto bail;

    if (osb->local_alloc_bits >= osb->bitmap_cpg) {
        mlog(ML_NOTICE, "Requested local alloc window %d is larger "
             "than max possible %u. Using defaults.\n",
             osb->local_alloc_bits, (osb->bitmap_cpg - 1));
        osb->local_alloc_bits =
            ocfs2_megabytes_to_clusters(osb->sb,
                            ocfs2_la_default_mb(osb));
    }

    /* read the alloc off disk */
    inode = ocfs2_get_system_file_inode(osb, LOCAL_ALLOC_SYSTEM_INODE,
                        osb->slot_num);
    if (!inode) {
        status = -EINVAL;
        mlog_errno(status);
        goto bail;
    }

    status = ocfs2_read_inode_block_full(inode, &alloc_bh,
                         OCFS2_BH_IGNORE_CACHE);
    if (status < 0) {
        mlog_errno(status);
        goto bail;
    }

    alloc = (struct ocfs2_dinode *) alloc_bh->b_data;
    la = OCFS2_LOCAL_ALLOC(alloc);

    if (!(le32_to_cpu(alloc->i_flags) &
        (OCFS2_LOCAL_ALLOC_FL|OCFS2_BITMAP_FL))) {
        mlog(ML_ERROR, "Invalid local alloc inode, %llu\n",
             (unsigned long long)OCFS2_I(inode)->ip_blkno);
        status = -EINVAL;
        goto bail;
    }

    if ((la->la_size == 0) ||
        (le16_to_cpu(la->la_size) > ocfs2_local_alloc_size(inode->i_sb))) {
        mlog(ML_ERROR, "Local alloc size is invalid (la_size = %u)\n",
             le16_to_cpu(la->la_size));
        status = -EINVAL;
        goto bail;
    }

    /* do a little verification. */
    num_used = ocfs2_local_alloc_count_bits(alloc);

    /* hopefully the local alloc has always been recovered before
     * we load it. */
    if (num_used
        || alloc->id1.bitmap1.i_used
        || alloc->id1.bitmap1.i_total
        || la->la_bm_off)
        mlog(ML_ERROR, "Local alloc hasn't been recovered!\n"
             "found = %u, set = %u, taken = %u, off = %u\n",
             num_used, le32_to_cpu(alloc->id1.bitmap1.i_used),
             le32_to_cpu(alloc->id1.bitmap1.i_total),
             OCFS2_LOCAL_ALLOC(alloc)->la_bm_off);

    osb->local_alloc_bh = alloc_bh;
    osb->local_alloc_state = OCFS2_LA_ENABLED;

bail:
    if (status < 0)
        brelse(alloc_bh);
    if (inode)
        iput(inode);

    trace_ocfs2_load_local_alloc(osb->local_alloc_bits);

    if (status)
        mlog_errno(status);
    return status;
}

/*
 * return any unused bits to the bitmap and write out a clean
 * local_alloc.
 *
 * local_alloc_bh is optional. If not passed, we will simply use the
 * one off osb. If you do pass it however, be warned that it *will* be
 * returned brelse'd and NULL'd out.*/
void ocfs2_shutdown_local_alloc(struct ocfs2_super *osb)
{
    int status;
    handle_t *handle;
    struct inode *local_alloc_inode = NULL;
    struct buffer_head *bh = NULL;
    struct buffer_head *main_bm_bh = NULL;
    struct inode *main_bm_inode = NULL;
    struct ocfs2_dinode *alloc_copy = NULL;
    struct ocfs2_dinode *alloc = NULL;

    cancel_delayed_work(&osb->la_enable_wq);
    flush_workqueue(ocfs2_wq);

    if (osb->local_alloc_state == OCFS2_LA_UNUSED)
        goto out;

    local_alloc_inode =
        ocfs2_get_system_file_inode(osb,
                        LOCAL_ALLOC_SYSTEM_INODE,
                        osb->slot_num);
    if (!local_alloc_inode) {
        status = -ENOENT;
        mlog_errno(status);
        goto out;
    }

    osb->local_alloc_state = OCFS2_LA_DISABLED;

    ocfs2_resmap_uninit(&osb->osb_la_resmap);

    main_bm_inode = ocfs2_get_system_file_inode(osb,
                            GLOBAL_BITMAP_SYSTEM_INODE,
                            OCFS2_INVALID_SLOT);
    if (!main_bm_inode) {
        status = -EINVAL;
        mlog_errno(status);
        goto out;
    }

    mutex_lock(&main_bm_inode->i_mutex);

    status = ocfs2_inode_lock(main_bm_inode, &main_bm_bh, 1);
    if (status < 0) {
        mlog_errno(status);
        goto out_mutex;
    }

    /* WINDOW_MOVE_CREDITS is a bit heavy... */
    handle = ocfs2_start_trans(osb, OCFS2_WINDOW_MOVE_CREDITS);
    if (IS_ERR(handle)) {
        mlog_errno(PTR_ERR(handle));
        handle = NULL;
        goto out_unlock;
    }

    bh = osb->local_alloc_bh;
    alloc = (struct ocfs2_dinode *) bh->b_data;

    alloc_copy = kmalloc(bh->b_size, GFP_NOFS);
    if (!alloc_copy) {
        status = -ENOMEM;
        goto out_commit;
    }
    memcpy(alloc_copy, alloc, bh->b_size);

    status = ocfs2_journal_access_di(handle, INODE_CACHE(local_alloc_inode),
                     bh, OCFS2_JOURNAL_ACCESS_WRITE);
    if (status < 0) {
        mlog_errno(status);
        goto out_commit;
    }

    ocfs2_clear_local_alloc(alloc);
    ocfs2_journal_dirty(handle, bh);

    brelse(bh);
    osb->local_alloc_bh = NULL;
    osb->local_alloc_state = OCFS2_LA_UNUSED;

    status = ocfs2_sync_local_to_main(osb, handle, alloc_copy,
                      main_bm_inode, main_bm_bh);
    if (status < 0)
        mlog_errno(status);

out_commit:
    ocfs2_commit_trans(osb, handle);

out_unlock:
    brelse(main_bm_bh);

    ocfs2_inode_unlock(main_bm_inode, 1);

out_mutex:
    mutex_unlock(&main_bm_inode->i_mutex);
    iput(main_bm_inode);

out:
    if (local_alloc_inode)
        iput(local_alloc_inode);

    if (alloc_copy)
        kfree(alloc_copy);
}

/*
 * We want to free the bitmap bits outside of any recovery context as
 * we'll need a cluster lock to do so, but we must clear the local
 * alloc before giving up the recovered nodes journal. To solve this,
 * we kmalloc a copy of the local alloc before it's change for the
 * caller to process with ocfs2_complete_local_alloc_recovery
 */
int ocfs2_begin_local_alloc_recovery(struct ocfs2_super *osb,
                     int slot_num,
                     struct ocfs2_dinode **alloc_copy)
{
    int status = 0;
    struct buffer_head *alloc_bh = NULL;
    struct inode *inode = NULL;
    struct ocfs2_dinode *alloc;

    trace_ocfs2_begin_local_alloc_recovery(slot_num);

    *alloc_copy = NULL;

    inode = ocfs2_get_system_file_inode(osb,
                        LOCAL_ALLOC_SYSTEM_INODE,
                        slot_num);
    if (!inode) {
        status = -EINVAL;
        mlog_errno(status);
        goto bail;
    }

    mutex_lock(&inode->i_mutex);

    status = ocfs2_read_inode_block_full(inode, &alloc_bh,
                         OCFS2_BH_IGNORE_CACHE);
    if (status < 0) {
        mlog_errno(status);
        goto bail;
    }

    *alloc_copy = kmalloc(alloc_bh->b_size, GFP_KERNEL);
    if (!(*alloc_copy)) {
        status = -ENOMEM;
        goto bail;
    }
    memcpy((*alloc_copy), alloc_bh->b_data, alloc_bh->b_size);

    alloc = (struct ocfs2_dinode *) alloc_bh->b_data;
    ocfs2_clear_local_alloc(alloc);

    ocfs2_compute_meta_ecc(osb->sb, alloc_bh->b_data, &alloc->i_check);
    status = ocfs2_write_block(osb, alloc_bh, INODE_CACHE(inode));
    if (status < 0)
        mlog_errno(status);

bail:
    if ((status < 0) && (*alloc_copy)) {
        kfree(*alloc_copy);
        *alloc_copy = NULL;
    }

    brelse(alloc_bh);

    if (inode) {
        mutex_unlock(&inode->i_mutex);
        iput(inode);
    }

    if (status)
        mlog_errno(status);
    return status;
}

/*
 * Step 2: By now, we've completed the journal recovery, we've stamped
 * a clean local alloc on disk and dropped the node out of the
 * recovery map. Dlm locks will no longer stall, so lets clear out the
 * main bitmap.
 */
int ocfs2_complete_local_alloc_recovery(struct ocfs2_super *osb,
                    struct ocfs2_dinode *alloc)
{
    int status;
    handle_t *handle;
    struct buffer_head *main_bm_bh = NULL;
    struct inode *main_bm_inode;

    main_bm_inode = ocfs2_get_system_file_inode(osb,
                            GLOBAL_BITMAP_SYSTEM_INODE,
                            OCFS2_INVALID_SLOT);
    if (!main_bm_inode) {
        status = -EINVAL;
        mlog_errno(status);
        goto out;
    }

    mutex_lock(&main_bm_inode->i_mutex);

    status = ocfs2_inode_lock(main_bm_inode, &main_bm_bh, 1);
    if (status < 0) {
        mlog_errno(status);
        goto out_mutex;
    }

    handle = ocfs2_start_trans(osb, OCFS2_WINDOW_MOVE_CREDITS);
    if (IS_ERR(handle)) {
        status = PTR_ERR(handle);
        handle = NULL;
        mlog_errno(status);
        goto out_unlock;
    }

    /* we want the bitmap change to be recorded on disk asap */
    handle->h_sync = 1;

    status = ocfs2_sync_local_to_main(osb, handle, alloc,
                      main_bm_inode, main_bm_bh);
    if (status < 0)
        mlog_errno(status);

    ocfs2_commit_trans(osb, handle);

out_unlock:
    ocfs2_inode_unlock(main_bm_inode, 1);

out_mutex:
    mutex_unlock(&main_bm_inode->i_mutex);

    brelse(main_bm_bh);

    iput(main_bm_inode);

out:
    if (!status)
        ocfs2_init_steal_slots(osb);
    if (status)
        mlog_errno(status);
    return status;
}

/*
 * make sure we've got at least bits_wanted contiguous bits in the
 * local alloc. You lose them when you drop i_mutex.
 *
 * We will add ourselves to the transaction passed in, but may start
 * our own in order to shift windows.
 */
int ocfs2_reserve_local_alloc_bits(struct ocfs2_super *osb,
                   u32 bits_wanted,
                   struct ocfs2_alloc_context *ac)
{
    int status;
    struct ocfs2_dinode *alloc;
    struct inode *local_alloc_inode;
    unsigned int free_bits;

    BUG_ON(!ac);

    local_alloc_inode =
        ocfs2_get_system_file_inode(osb,
                        LOCAL_ALLOC_SYSTEM_INODE,
                        osb->slot_num);
    if (!local_alloc_inode) {
        status = -ENOENT;
        mlog_errno(status);
        goto bail;
    }

    mutex_lock(&local_alloc_inode->i_mutex);

    /*
     * We must double check state and allocator bits because
     * another process may have changed them while holding i_mutex.
     */
    spin_lock(&osb->osb_lock);
    if (!ocfs2_la_state_enabled(osb) ||
        (bits_wanted > osb->local_alloc_bits)) {
        spin_unlock(&osb->osb_lock);
        status = -ENOSPC;
        goto bail;
    }
    spin_unlock(&osb->osb_lock);

    alloc = (struct ocfs2_dinode *) osb->local_alloc_bh->b_data;

#ifdef CONFIG_OCFS2_DEBUG_FS
    if (le32_to_cpu(alloc->id1.bitmap1.i_used) !=
        ocfs2_local_alloc_count_bits(alloc)) {
        ocfs2_error(osb->sb, "local alloc inode %llu says it has "
                "%u free bits, but a count shows %u",
                (unsigned long long)le64_to_cpu(alloc->i_blkno),
                le32_to_cpu(alloc->id1.bitmap1.i_used),
                ocfs2_local_alloc_count_bits(alloc));
        status = -EIO;
        goto bail;
    }
#endif

    free_bits = le32_to_cpu(alloc->id1.bitmap1.i_total) -
        le32_to_cpu(alloc->id1.bitmap1.i_used);
    if (bits_wanted > free_bits) {
        /* uhoh, window change time. */
        status =
            ocfs2_local_alloc_slide_window(osb, local_alloc_inode);
        if (status < 0) {
            if (status != -ENOSPC)
                mlog_errno(status);
            goto bail;
        }

        /*
         * Under certain conditions, the window slide code
         * might have reduced the number of bits available or
         * disabled the the local alloc entirely. Re-check
         * here and return -ENOSPC if necessary.
         */
        status = -ENOSPC;
        if (!ocfs2_la_state_enabled(osb))
            goto bail;

        free_bits = le32_to_cpu(alloc->id1.bitmap1.i_total) -
            le32_to_cpu(alloc->id1.bitmap1.i_used);
        if (bits_wanted > free_bits)
            goto bail;
    }

    ac->ac_inode = local_alloc_inode;
    /* We should never use localalloc from another slot */
    ac->ac_alloc_slot = osb->slot_num;
    ac->ac_which = OCFS2_AC_USE_LOCAL;
    get_bh(osb->local_alloc_bh);
    ac->ac_bh = osb->local_alloc_bh;
    status = 0;
bail:
    if (status < 0 && local_alloc_inode) {
        mutex_unlock(&local_alloc_inode->i_mutex);
        iput(local_alloc_inode);
    }

    trace_ocfs2_reserve_local_alloc_bits(
        (unsigned long long)ac->ac_max_block,
        bits_wanted, osb->slot_num, status);

    if (status)
        mlog_errno(status);
    return status;
}

int ocfs2_claim_local_alloc_bits(struct ocfs2_super *osb,
                 handle_t *handle,
                 struct ocfs2_alloc_context *ac,
                 u32 bits_wanted,
                 u32 *bit_off,
                 u32 *num_bits)
{
    int status, start;
    struct inode *local_alloc_inode;
    void *bitmap;
    struct ocfs2_dinode *alloc;
    struct ocfs2_local_alloc *la;

    BUG_ON(ac->ac_which != OCFS2_AC_USE_LOCAL);

    local_alloc_inode = ac->ac_inode;
    alloc = (struct ocfs2_dinode *) osb->local_alloc_bh->b_data;
    la = OCFS2_LOCAL_ALLOC(alloc);

    start = ocfs2_local_alloc_find_clear_bits(osb, alloc, &bits_wanted,
                          ac->ac_resv);
    if (start == -1) {
        /* TODO: Shouldn't we just BUG here? */
        status = -ENOSPC;
        mlog_errno(status);
        goto bail;
    }

    bitmap = la->la_bitmap;
    *bit_off = le32_to_cpu(la->la_bm_off) + start;
    *num_bits = bits_wanted;

    status = ocfs2_journal_access_di(handle,
                     INODE_CACHE(local_alloc_inode),
                     osb->local_alloc_bh,
                     OCFS2_JOURNAL_ACCESS_WRITE);
    if (status < 0) {
        mlog_errno(status);
        goto bail;
    }

    ocfs2_resmap_claimed_bits(&osb->osb_la_resmap, ac->ac_resv, start,
                  bits_wanted);

    while(bits_wanted--)
        ocfs2_set_bit(start++, bitmap);

    le32_add_cpu(&alloc->id1.bitmap1.i_used, *num_bits);
    ocfs2_journal_dirty(handle, osb->local_alloc_bh);

bail:
    if (status)
        mlog_errno(status);
    return status;
}

static u32 ocfs2_local_alloc_count_bits(struct ocfs2_dinode *alloc)
{
    u32 count;
    struct ocfs2_local_alloc *la = OCFS2_LOCAL_ALLOC(alloc);

    count = memweight(la->la_bitmap, le16_to_cpu(la->la_size));

    trace_ocfs2_local_alloc_count_bits(count);
    return count;
}

static int ocfs2_local_alloc_find_clear_bits(struct ocfs2_super *osb,
                     struct ocfs2_dinode *alloc,
                     u32 *numbits,
                     struct ocfs2_alloc_reservation *resv)
{
    int numfound, bitoff, left, startoff, lastzero;
    int local_resv = 0;
    struct ocfs2_alloc_reservation r;
    void *bitmap = NULL;
    struct ocfs2_reservation_map *resmap = &osb->osb_la_resmap;

    if (!alloc->id1.bitmap1.i_total) {
        bitoff = -1;
        goto bail;
    }

    if (!resv) {
        local_resv = 1;
        ocfs2_resv_init_once(&r);
        ocfs2_resv_set_type(&r, OCFS2_RESV_FLAG_TMP);
        resv = &r;
    }

    numfound = *numbits;
    if (ocfs2_resmap_resv_bits(resmap, resv, &bitoff, &numfound) == 0) {
        if (numfound < *numbits)
            *numbits = numfound;
        goto bail;
    }

    /*
     * Code error. While reservations are enabled, local
     * allocation should _always_ go through them.
     */
    BUG_ON(osb->osb_resv_level != 0);

    /*
     * Reservations are disabled. Handle this the old way.
     */

    bitmap = OCFS2_LOCAL_ALLOC(alloc)->la_bitmap;

    numfound = bitoff = startoff = 0;
    lastzero = -1;
    left = le32_to_cpu(alloc->id1.bitmap1.i_total);
    while ((bitoff = ocfs2_find_next_zero_bit(bitmap, left, startoff)) != -1) {
        if (bitoff == left) {
            /* mlog(0, "bitoff (%d) == left", bitoff); */
            break;
        }
        /* mlog(0, "Found a zero: bitoff = %d, startoff = %d, "
           "numfound = %d\n", bitoff, startoff, numfound);*/

        /* Ok, we found a zero bit... is it contig. or do we
         * start over?*/
        if (bitoff == startoff) {
            /* we found a zero */
            numfound++;
            startoff++;
        } else {
            /* got a zero after some ones */
            numfound = 1;
            startoff = bitoff+1;
        }
        /* we got everything we needed */
        if (numfound == *numbits) {
            /* mlog(0, "Found it all!\n"); */
            break;
        }
    }

    trace_ocfs2_local_alloc_find_clear_bits_search_bitmap(bitoff, numfound);

    if (numfound == *numbits)
        bitoff = startoff - numfound;
    else
        bitoff = -1;

bail:
    if (local_resv)
        ocfs2_resv_discard(resmap, resv);

    trace_ocfs2_local_alloc_find_clear_bits(*numbits,
        le32_to_cpu(alloc->id1.bitmap1.i_total),
        bitoff, numfound);

    return bitoff;
}

static void ocfs2_clear_local_alloc(struct ocfs2_dinode *alloc)
{
    struct ocfs2_local_alloc *la = OCFS2_LOCAL_ALLOC(alloc);
    int i;

    alloc->id1.bitmap1.i_total = 0;
    alloc->id1.bitmap1.i_used = 0;
    la->la_bm_off = 0;
    for(i = 0; i < le16_to_cpu(la->la_size); i++)
        la->la_bitmap[i] = 0;
}

#if 0
/* turn this on and uncomment below to aid debugging window shifts. */
static void ocfs2_verify_zero_bits(unsigned long *bitmap,
                   unsigned int start,
                   unsigned int count)
{
    unsigned int tmp = count;
    while(tmp--) {
        if (ocfs2_test_bit(start + tmp, bitmap)) {
            printk("ocfs2_verify_zero_bits: start = %u, count = "
                   "%u\n", start, count);
            printk("ocfs2_verify_zero_bits: bit %u is set!",
                   start + tmp);
            BUG();
        }
    }
}
#endif

/*
 * sync the local alloc to main bitmap.
 *
 * assumes you've already locked the main bitmap -- the bitmap inode
 * passed is used for caching.
 */
static int ocfs2_sync_local_to_main(struct ocfs2_super *osb,
                    handle_t *handle,
                    struct ocfs2_dinode *alloc,
                    struct inode *main_bm_inode,
                    struct buffer_head *main_bm_bh)
{
    int status = 0;
    int bit_off, left, count, start;
    u64 la_start_blk;
    u64 blkno;
    void *bitmap;
    struct ocfs2_local_alloc *la = OCFS2_LOCAL_ALLOC(alloc);

    trace_ocfs2_sync_local_to_main(
         le32_to_cpu(alloc->id1.bitmap1.i_total),
         le32_to_cpu(alloc->id1.bitmap1.i_used));

    if (!alloc->id1.bitmap1.i_total) {
        goto bail;
    }

    if (le32_to_cpu(alloc->id1.bitmap1.i_used) ==
        le32_to_cpu(alloc->id1.bitmap1.i_total)) {
        goto bail;
    }

    la_start_blk = ocfs2_clusters_to_blocks(osb->sb,
                        le32_to_cpu(la->la_bm_off));
    bitmap = la->la_bitmap;
    start = count = bit_off = 0;
    left = le32_to_cpu(alloc->id1.bitmap1.i_total);

    while ((bit_off = ocfs2_find_next_zero_bit(bitmap, left, start))
           != -1) {
        if ((bit_off < left) && (bit_off == start)) {
            count++;
            start++;
            continue;
        }
        if (count) {
            blkno = la_start_blk +
                ocfs2_clusters_to_blocks(osb->sb,
                             start - count);

            trace_ocfs2_sync_local_to_main_free(
                 count, start - count,
                 (unsigned long long)la_start_blk,
                 (unsigned long long)blkno);

            status = ocfs2_release_clusters(handle,
                            main_bm_inode,
                            main_bm_bh, blkno,
                            count);
            if (status < 0) {
                mlog_errno(status);
                goto bail;
            }
        }
        if (bit_off >= left)
            break;
        count = 1;
        start = bit_off + 1;
    }

bail:
    if (status)
        mlog_errno(status);
    return status;
}

enum ocfs2_la_event {
    OCFS2_LA_EVENT_SLIDE,       /* Normal window slide. */
    OCFS2_LA_EVENT_FRAGMENTED,  /* The global bitmap has
                     * enough bits theoretically
                     * free, but a contiguous
                     * allocation could not be
                     * found. */
    OCFS2_LA_EVENT_ENOSPC,      /* Global bitmap doesn't have
                     * enough bits free to satisfy
                     * our request. */
};
#define OCFS2_LA_ENABLE_INTERVAL (30 * HZ)
/*
 * Given an event, calculate the size of our next local alloc window.
 *
 * This should always be called under i_mutex of the local alloc inode
 * so that local alloc disabling doesn't race with processes trying to
 * use the allocator.
 *
 * Returns the state which the local alloc was left in. This value can
 * be ignored by some paths.
 */
static int ocfs2_recalc_la_window(struct ocfs2_super *osb,
                  enum ocfs2_la_event event)
{
    unsigned int bits;
    int state;

    spin_lock(&osb->osb_lock);
    if (osb->local_alloc_state == OCFS2_LA_DISABLED) {
        WARN_ON_ONCE(osb->local_alloc_state == OCFS2_LA_DISABLED);
        goto out_unlock;
    }

    /*
     * ENOSPC and fragmentation are treated similarly for now.
     */
    if (event == OCFS2_LA_EVENT_ENOSPC ||
        event == OCFS2_LA_EVENT_FRAGMENTED) {
        /*
         * We ran out of contiguous space in the primary
         * bitmap. Drastically reduce the number of bits used
         * by local alloc until we have to disable it.
         */
        bits = osb->local_alloc_bits >> 1;
        if (bits > ocfs2_megabytes_to_clusters(osb->sb, 1)) {
            /*
             * By setting state to THROTTLED, we'll keep
             * the number of local alloc bits used down
             * until an event occurs which would give us
             * reason to assume the bitmap situation might
             * have changed.
             */
            osb->local_alloc_state = OCFS2_LA_THROTTLED;
            osb->local_alloc_bits = bits;
        } else {
            osb->local_alloc_state = OCFS2_LA_DISABLED;
        }
        queue_delayed_work(ocfs2_wq, &osb->la_enable_wq,
                   OCFS2_LA_ENABLE_INTERVAL);
        goto out_unlock;
    }

    /*
     * Don't increase the size of the local alloc window until we
     * know we might be able to fulfill the request. Otherwise, we
     * risk bouncing around the global bitmap during periods of
     * low space.
     */
    if (osb->local_alloc_state != OCFS2_LA_THROTTLED)
        osb->local_alloc_bits = osb->local_alloc_default_bits;

out_unlock:
    state = osb->local_alloc_state;
    spin_unlock(&osb->osb_lock);

    return state;
}

static int ocfs2_local_alloc_reserve_for_window(struct ocfs2_super *osb,
                        struct ocfs2_alloc_context **ac,
                        struct inode **bitmap_inode,
                        struct buffer_head **bitmap_bh)
{
    int status;

    *ac = kzalloc(sizeof(struct ocfs2_alloc_context), GFP_KERNEL);
    if (!(*ac)) {
        status = -ENOMEM;
        mlog_errno(status);
        goto bail;
    }

retry_enospc:
    (*ac)->ac_bits_wanted = osb->local_alloc_default_bits;
    status = ocfs2_reserve_cluster_bitmap_bits(osb, *ac);
    if (status == -ENOSPC) {
        if (ocfs2_recalc_la_window(osb, OCFS2_LA_EVENT_ENOSPC) ==
            OCFS2_LA_DISABLED)
            goto bail;

        ocfs2_free_ac_resource(*ac);
        memset(*ac, 0, sizeof(struct ocfs2_alloc_context));
        goto retry_enospc;
    }
    if (status < 0) {
        mlog_errno(status);
        goto bail;
    }

    *bitmap_inode = (*ac)->ac_inode;
    igrab(*bitmap_inode);
    *bitmap_bh = (*ac)->ac_bh;
    get_bh(*bitmap_bh);
    status = 0;
bail:
    if ((status < 0) && *ac) {
        ocfs2_free_alloc_context(*ac);
        *ac = NULL;
    }

    if (status)
        mlog_errno(status);
    return status;
}

/*
 * pass it the bitmap lock in lock_bh if you have it.
 */
static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
                    handle_t *handle,
                    struct ocfs2_alloc_context *ac)
{
    int status = 0;
    u32 cluster_off, cluster_count;
    struct ocfs2_dinode *alloc = NULL;
    struct ocfs2_local_alloc *la;

    alloc = (struct ocfs2_dinode *) osb->local_alloc_bh->b_data;
    la = OCFS2_LOCAL_ALLOC(alloc);

    trace_ocfs2_local_alloc_new_window(
        le32_to_cpu(alloc->id1.bitmap1.i_total),
        osb->local_alloc_bits);

    /* Instruct the allocation code to try the most recently used
     * cluster group. We'll re-record the group used this pass
     * below. */
    ac->ac_last_group = osb->la_last_gd;

    /* we used the generic suballoc reserve function, but we set
     * everything up nicely, so there's no reason why we can't use
     * the more specific cluster api to claim bits. */
    status = ocfs2_claim_clusters(handle, ac, osb->local_alloc_bits,
                      &cluster_off, &cluster_count);
    if (status == -ENOSPC) {
retry_enospc:
        /*
         * Note: We could also try syncing the journal here to
         * allow use of any free bits which the current
         * transaction can't give us access to. --Mark
         */
        if (ocfs2_recalc_la_window(osb, OCFS2_LA_EVENT_FRAGMENTED) ==
            OCFS2_LA_DISABLED)
            goto bail;

        ac->ac_bits_wanted = osb->local_alloc_default_bits;
        status = ocfs2_claim_clusters(handle, ac,
                          osb->local_alloc_bits,
                          &cluster_off,
                          &cluster_count);
        if (status == -ENOSPC)
            goto retry_enospc;
        /*
         * We only shrunk the *minimum* number of in our
         * request - it's entirely possible that the allocator
         * might give us more than we asked for.
         */
        if (status == 0) {
            spin_lock(&osb->osb_lock);
            osb->local_alloc_bits = cluster_count;
            spin_unlock(&osb->osb_lock);
        }
    }
    if (status < 0) {
        if (status != -ENOSPC)
            mlog_errno(status);
        goto bail;
    }

    osb->la_last_gd = ac->ac_last_group;

    la->la_bm_off = cpu_to_le32(cluster_off);
    alloc->id1.bitmap1.i_total = cpu_to_le32(cluster_count);
    /* just in case... In the future when we find space ourselves,
     * we don't have to get all contiguous -- but we'll have to
     * set all previously used bits in bitmap and update
     * la_bits_set before setting the bits in the main bitmap. */
    alloc->id1.bitmap1.i_used = 0;
    memset(OCFS2_LOCAL_ALLOC(alloc)->la_bitmap, 0,
           le16_to_cpu(la->la_size));

    ocfs2_resmap_restart(&osb->osb_la_resmap, cluster_count,
                 OCFS2_LOCAL_ALLOC(alloc)->la_bitmap);

    trace_ocfs2_local_alloc_new_window_result(
        OCFS2_LOCAL_ALLOC(alloc)->la_bm_off,
        le32_to_cpu(alloc->id1.bitmap1.i_total));

bail:
    if (status)
        mlog_errno(status);
    return status;
}

/* Note that we do *NOT* lock the local alloc inode here as
 * it's been locked already for us. */
static int ocfs2_local_alloc_slide_window(struct ocfs2_super *osb,
                      struct inode *local_alloc_inode)
{
    int status = 0;
    struct buffer_head *main_bm_bh = NULL;
    struct inode *main_bm_inode = NULL;
    handle_t *handle = NULL;
    struct ocfs2_dinode *alloc;
    struct ocfs2_dinode *alloc_copy = NULL;
    struct ocfs2_alloc_context *ac = NULL;

    ocfs2_recalc_la_window(osb, OCFS2_LA_EVENT_SLIDE);

    /* This will lock the main bitmap for us. */
    status = ocfs2_local_alloc_reserve_for_window(osb,
                              &ac,
                              &main_bm_inode,
                              &main_bm_bh);
    if (status < 0) {
        if (status != -ENOSPC)
            mlog_errno(status);
        goto bail;
    }

    handle = ocfs2_start_trans(osb, OCFS2_WINDOW_MOVE_CREDITS);
    if (IS_ERR(handle)) {
        status = PTR_ERR(handle);
        handle = NULL;
        mlog_errno(status);
        goto bail;
    }

    alloc = (struct ocfs2_dinode *) osb->local_alloc_bh->b_data;

    /* We want to clear the local alloc before doing anything
     * else, so that if we error later during this operation,
     * local alloc shutdown won't try to double free main bitmap
     * bits. Make a copy so the sync function knows which bits to
     * free. */
    alloc_copy = kmalloc(osb->local_alloc_bh->b_size, GFP_NOFS);
    if (!alloc_copy) {
        status = -ENOMEM;
        mlog_errno(status);
        goto bail;
    }
    memcpy(alloc_copy, alloc, osb->local_alloc_bh->b_size);

    status = ocfs2_journal_access_di(handle,
                     INODE_CACHE(local_alloc_inode),
                     osb->local_alloc_bh,
                     OCFS2_JOURNAL_ACCESS_WRITE);
    if (status < 0) {
        mlog_errno(status);
        goto bail;
    }

    ocfs2_clear_local_alloc(alloc);
    ocfs2_journal_dirty(handle, osb->local_alloc_bh);

    status = ocfs2_sync_local_to_main(osb, handle, alloc_copy,
                      main_bm_inode, main_bm_bh);
    if (status < 0) {
        mlog_errno(status);
        goto bail;
    }

    status = ocfs2_local_alloc_new_window(osb, handle, ac);
    if (status < 0) {
        if (status != -ENOSPC)
            mlog_errno(status);
        goto bail;
    }

    atomic_inc(&osb->alloc_stats.moves);

bail:
    if (handle)
        ocfs2_commit_trans(osb, handle);

    brelse(main_bm_bh);

    if (main_bm_inode)
        iput(main_bm_inode);

    if (alloc_copy)
        kfree(alloc_copy);

    if (ac)
        ocfs2_free_alloc_context(ac);

    if (status)
        mlog_errno(status);
    return status;
}