slob.c

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/*
 * SLOB Allocator: Simple List Of Blocks
 *
 * Matt Mackall <[email protected]> 12/30/03
 *
 * NUMA support by Paul Mundt, 2007.
 *
 * How SLOB works:
 *
 * The core of SLOB is a traditional K&R style heap allocator, with
 * support for returning aligned objects. The granularity of this
 * allocator is as little as 2 bytes, however typically most architectures
 * will require 4 bytes on 32-bit and 8 bytes on 64-bit.
 *
 * The slob heap is a set of linked list of pages from alloc_pages(),
 * and within each page, there is a singly-linked list of free blocks
 * (slob_t). The heap is grown on demand. To reduce fragmentation,
 * heap pages are segregated into three lists, with objects less than
 * 256 bytes, objects less than 1024 bytes, and all other objects.
 *
 * Allocation from heap involves first searching for a page with
 * sufficient free blocks (using a next-fit-like approach) followed by
 * a first-fit scan of the page. Deallocation inserts objects back
 * into the free list in address order, so this is effectively an
 * address-ordered first fit.
 *
 * Above this is an implementation of kmalloc/kfree. Blocks returned
 * from kmalloc are prepended with a 4-byte header with the kmalloc size.
 * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
 * alloc_pages() directly, allocating compound pages so the page order
 * does not have to be separately tracked, and also stores the exact
 * allocation size in page->private so that it can be used to accurately
 * provide ksize(). These objects are detected in kfree() because slob_page()
 * is false for them.
 *
 * SLAB is emulated on top of SLOB by simply calling constructors and
 * destructors for every SLAB allocation. Objects are returned with the
 * 4-byte alignment unless the SLAB_HWCACHE_ALIGN flag is set, in which
 * case the low-level allocator will fragment blocks to create the proper
 * alignment. Again, objects of page-size or greater are allocated by
 * calling alloc_pages(). As SLAB objects know their size, no separate
 * size bookkeeping is necessary and there is essentially no allocation
 * space overhead, and compound pages aren't needed for multi-page
 * allocations.
 *
 * NUMA support in SLOB is fairly simplistic, pushing most of the real
 * logic down to the page allocator, and simply doing the node accounting
 * on the upper levels. In the event that a node id is explicitly
 * provided, alloc_pages_exact_node() with the specified node id is used
 * instead. The common case (or when the node id isn't explicitly provided)
 * will default to the current node, as per numa_node_id().
 *
 * Node aware pages are still inserted in to the global freelist, and
 * these are scanned for by matching against the node id encoded in the
 * page flags. As a result, block allocations that can be satisfied from
 * the freelist will only be done so on pages residing on the same node,
 * in order to prevent random node placement.
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include "slab.h"

#include <linux/mm.h>
#include <linux/swap.h> /* struct reclaim_state */
#include <linux/cache.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/rcupdate.h>
#include <linux/list.h>
#include <linux/kmemleak.h>

#include <trace/events/kmem.h>

#include <linux/atomic.h>

/*
 * slob_block has a field 'units', which indicates size of block if +ve,
 * or offset of next block if -ve (in SLOB_UNITs).
 *
 * Free blocks of size 1 unit simply contain the offset of the next block.
 * Those with larger size contain their size in the first SLOB_UNIT of
 * memory, and the offset of the next free block in the second SLOB_UNIT.
 */
#if PAGE_SIZE <= (32767 * 2)
typedef s16 slobidx_t;
#else
typedef s32 slobidx_t;
#endif

struct slob_block {
    slobidx_t units;
};
typedef struct slob_block slob_t;

/*
 * All partially free slob pages go on these lists.
 */
#define SLOB_BREAK1 256
#define SLOB_BREAK2 1024
static LIST_HEAD(free_slob_small);
static LIST_HEAD(free_slob_medium);
static LIST_HEAD(free_slob_large);

/*
 * slob_page_free: true for pages on free_slob_pages list.
 */
static inline int slob_page_free(struct page *sp)
{
    return PageSlobFree(sp);
}

static void set_slob_page_free(struct page *sp, struct list_head *list)
{
    list_add(&sp->list, list);
    __SetPageSlobFree(sp);
}

static inline void clear_slob_page_free(struct page *sp)
{
    list_del(&sp->list);
    __ClearPageSlobFree(sp);
}

#define SLOB_UNIT sizeof(slob_t)
#define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
#define SLOB_ALIGN L1_CACHE_BYTES

/*
 * struct slob_rcu is inserted at the tail of allocated slob blocks, which
 * were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
 * the block using call_rcu.
 */
struct slob_rcu {
    struct rcu_head head;
    int size;
};

/*
 * slob_lock protects all slob allocator structures.
 */
static DEFINE_SPINLOCK(slob_lock);

/*
 * Encode the given size and next info into a free slob block s.
 */
static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
{
    slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
    slobidx_t offset = next - base;

    if (size > 1) {
        s[0].units = size;
        s[1].units = offset;
    } else
        s[0].units = -offset;
}

/*
 * Return the size of a slob block.
 */
static slobidx_t slob_units(slob_t *s)
{
    if (s->units > 0)
        return s->units;
    return 1;
}

/*
 * Return the next free slob block pointer after this one.
 */
static slob_t *slob_next(slob_t *s)
{
    slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
    slobidx_t next;

    if (s[0].units < 0)
        next = -s[0].units;
    else
        next = s[1].units;
    return base+next;
}

/*
 * Returns true if s is the last free block in its page.
 */
static int slob_last(slob_t *s)
{
    return !((unsigned long)slob_next(s) & ~PAGE_MASK);
}

static void *slob_new_pages(gfp_t gfp, int order, int node)
{
    void *page;

#ifdef CONFIG_NUMA
    if (node != NUMA_NO_NODE)
        page = alloc_pages_exact_node(node, gfp, order);
    else
#endif
        page = alloc_pages(gfp, order);

    if (!page)
        return NULL;

    return page_address(page);
}

static void slob_free_pages(void *b, int order)
{
    if (current->reclaim_state)
        current->reclaim_state->reclaimed_slab += 1 << order;
    free_pages((unsigned long)b, order);
}

/*
 * Allocate a slob block within a given slob_page sp.
 */
static void *slob_page_alloc(struct page *sp, size_t size, int align)
{
    slob_t *prev, *cur, *aligned = NULL;
    int delta = 0, units = SLOB_UNITS(size);

    for (prev = NULL, cur = sp->freelist; ; prev = cur, cur = slob_next(cur)) {
        slobidx_t avail = slob_units(cur);

        if (align) {
            aligned = (slob_t *)ALIGN((unsigned long)cur, align);
            delta = aligned - cur;
        }
        if (avail >= units + delta) { /* room enough? */
            slob_t *next;

            if (delta) { /* need to fragment head to align? */
                next = slob_next(cur);
                set_slob(aligned, avail - delta, next);
                set_slob(cur, delta, aligned);
                prev = cur;
                cur = aligned;
                avail = slob_units(cur);
            }

            next = slob_next(cur);
            if (avail == units) { /* exact fit? unlink. */
                if (prev)
                    set_slob(prev, slob_units(prev), next);
                else
                    sp->freelist = next;
            } else { /* fragment */
                if (prev)
                    set_slob(prev, slob_units(prev), cur + units);
                else
                    sp->freelist = cur + units;
                set_slob(cur + units, avail - units, next);
            }

            sp->units -= units;
            if (!sp->units)
                clear_slob_page_free(sp);
            return cur;
        }
        if (slob_last(cur))
            return NULL;
    }
}

/*
 * slob_alloc: entry point into the slob allocator.
 */
static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
{
    struct page *sp;
    struct list_head *prev;
    struct list_head *slob_list;
    slob_t *b = NULL;
    unsigned long flags;

    if (size < SLOB_BREAK1)
        slob_list = &free_slob_small;
    else if (size < SLOB_BREAK2)
        slob_list = &free_slob_medium;
    else
        slob_list = &free_slob_large;

    spin_lock_irqsave(&slob_lock, flags);
    /* Iterate through each partially free page, try to find room */
    list_for_each_entry(sp, slob_list, list) {
#ifdef CONFIG_NUMA
        /*
         * If there's a node specification, search for a partial
         * page with a matching node id in the freelist.
         */
        if (node != NUMA_NO_NODE && page_to_nid(sp) != node)
            continue;
#endif
        /* Enough room on this page? */
        if (sp->units < SLOB_UNITS(size))
            continue;

        /* Attempt to alloc */
        prev = sp->list.prev;
        b = slob_page_alloc(sp, size, align);
        if (!b)
            continue;

        /* Improve fragment distribution and reduce our average
         * search time by starting our next search here. (see
         * Knuth vol 1, sec 2.5, pg 449) */
        if (prev != slob_list->prev &&
                slob_list->next != prev->next)
            list_move_tail(slob_list, prev->next);
        break;
    }
    spin_unlock_irqrestore(&slob_lock, flags);

    /* Not enough space: must allocate a new page */
    if (!b) {
        b = slob_new_pages(gfp & ~__GFP_ZERO, 0, node);
        if (!b)
            return NULL;
        sp = virt_to_page(b);
        __SetPageSlab(sp);

        spin_lock_irqsave(&slob_lock, flags);
        sp->units = SLOB_UNITS(PAGE_SIZE);
        sp->freelist = b;
        INIT_LIST_HEAD(&sp->list);
        set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE));
        set_slob_page_free(sp, slob_list);
        b = slob_page_alloc(sp, size, align);
        BUG_ON(!b);
        spin_unlock_irqrestore(&slob_lock, flags);
    }
    if (unlikely((gfp & __GFP_ZERO) && b))
        memset(b, 0, size);
    return b;
}

/*
 * slob_free: entry point into the slob allocator.
 */
static void slob_free(void *block, int size)
{
    struct page *sp;
    slob_t *prev, *next, *b = (slob_t *)block;
    slobidx_t units;
    unsigned long flags;
    struct list_head *slob_list;

    if (unlikely(ZERO_OR_NULL_PTR(block)))
        return;
    BUG_ON(!size);

    sp = virt_to_page(block);
    units = SLOB_UNITS(size);

    spin_lock_irqsave(&slob_lock, flags);

    if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
        /* Go directly to page allocator. Do not pass slob allocator */
        if (slob_page_free(sp))
            clear_slob_page_free(sp);
        spin_unlock_irqrestore(&slob_lock, flags);
        __ClearPageSlab(sp);
        reset_page_mapcount(sp);
        slob_free_pages(b, 0);
        return;
    }

    if (!slob_page_free(sp)) {
        /* This slob page is about to become partially free. Easy! */
        sp->units = units;
        sp->freelist = b;
        set_slob(b, units,
            (void *)((unsigned long)(b +
                    SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));
        if (size < SLOB_BREAK1)
            slob_list = &free_slob_small;
        else if (size < SLOB_BREAK2)
            slob_list = &free_slob_medium;
        else
            slob_list = &free_slob_large;
        set_slob_page_free(sp, slob_list);
        goto out;
    }

    /*
     * Otherwise the page is already partially free, so find reinsertion
     * point.
     */
    sp->units += units;

    if (b < (slob_t *)sp->freelist) {
        if (b + units == sp->freelist) {
            units += slob_units(sp->freelist);
            sp->freelist = slob_next(sp->freelist);
        }
        set_slob(b, units, sp->freelist);
        sp->freelist = b;
    } else {
        prev = sp->freelist;
        next = slob_next(prev);
        while (b > next) {
            prev = next;
            next = slob_next(prev);
        }

        if (!slob_last(prev) && b + units == next) {
            units += slob_units(next);
            set_slob(b, units, slob_next(next));
        } else
            set_slob(b, units, next);

        if (prev + slob_units(prev) == b) {
            units = slob_units(b) + slob_units(prev);
            set_slob(prev, units, slob_next(b));
        } else
            set_slob(prev, slob_units(prev), b);
    }
out:
    spin_unlock_irqrestore(&slob_lock, flags);
}

/*
 * End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
 */

static __always_inline void *
__do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
{
    unsigned int *m;
    int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
    void *ret;

    gfp &= gfp_allowed_mask;

    lockdep_trace_alloc(gfp);

    if (size < PAGE_SIZE - align) {
        if (!size)
            return ZERO_SIZE_PTR;

        m = slob_alloc(size + align, gfp, align, node);

        if (!m)
            return NULL;
        *m = size;
        ret = (void *)m + align;

        trace_kmalloc_node(caller, ret,
                   size, size + align, gfp, node);
    } else {
        unsigned int order = get_order(size);

        if (likely(order))
            gfp |= __GFP_COMP;
        ret = slob_new_pages(gfp, order, node);
        if (ret) {
            struct page *page;
            page = virt_to_page(ret);
            page->private = size;
        }

        trace_kmalloc_node(caller, ret,
                   size, PAGE_SIZE << order, gfp, node);
    }

    kmemleak_alloc(ret, size, 1, gfp);
    return ret;
}

void *__kmalloc_node(size_t size, gfp_t gfp, int node)
{
    return __do_kmalloc_node(size, gfp, node, _RET_IP_);
}
EXPORT_SYMBOL(__kmalloc_node);

#ifdef CONFIG_TRACING
void *__kmalloc_track_caller(size_t size, gfp_t gfp, unsigned long caller)
{
    return __do_kmalloc_node(size, gfp, NUMA_NO_NODE, caller);
}

#ifdef CONFIG_NUMA
void *__kmalloc_node_track_caller(size_t size, gfp_t gfp,
                    int node, unsigned long caller)
{
    return __do_kmalloc_node(size, gfp, node, caller);
}
#endif
#endif

void kfree(const void *block)
{
    struct page *sp;

    trace_kfree(_RET_IP_, block);

    if (unlikely(ZERO_OR_NULL_PTR(block)))
        return;
    kmemleak_free(block);

    sp = virt_to_page(block);
    if (PageSlab(sp)) {
        int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
        unsigned int *m = (unsigned int *)(block - align);
        slob_free(m, *m + align);
    } else
        put_page(sp);
}
EXPORT_SYMBOL(kfree);

/* can't use ksize for kmem_cache_alloc memory, only kmalloc */
size_t ksize(const void *block)
{
    struct page *sp;

    BUG_ON(!block);
    if (unlikely(block == ZERO_SIZE_PTR))
        return 0;

    sp = virt_to_page(block);
    if (PageSlab(sp)) {
        int align = max_t(size_t, ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
        unsigned int *m = (unsigned int *)(block - align);
        return SLOB_UNITS(*m) * SLOB_UNIT;
    } else
        return sp->private;
}
EXPORT_SYMBOL(ksize);

int __kmem_cache_create(struct kmem_cache *c, unsigned long flags)
{
    size_t align = c->size;

    if (flags & SLAB_DESTROY_BY_RCU) {
        /* leave room for rcu footer at the end of object */
        c->size += sizeof(struct slob_rcu);
    }
    c->flags = flags;
    /* ignore alignment unless it's forced */
    c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
    if (c->align < ARCH_SLAB_MINALIGN)
        c->align = ARCH_SLAB_MINALIGN;
    if (c->align < align)
        c->align = align;

    return 0;
}

void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
{
    void *b;

    flags &= gfp_allowed_mask;

    lockdep_trace_alloc(flags);

    if (c->size < PAGE_SIZE) {
        b = slob_alloc(c->size, flags, c->align, node);
        trace_kmem_cache_alloc_node(_RET_IP_, b, c->size,
                        SLOB_UNITS(c->size) * SLOB_UNIT,
                        flags, node);
    } else {
        b = slob_new_pages(flags, get_order(c->size), node);
        trace_kmem_cache_alloc_node(_RET_IP_, b, c->size,
                        PAGE_SIZE << get_order(c->size),
                        flags, node);
    }

    if (c->ctor)
        c->ctor(b);

    kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);
    return b;
}
EXPORT_SYMBOL(kmem_cache_alloc_node);

static void __kmem_cache_free(void *b, int size)
{
    if (size < PAGE_SIZE)
        slob_free(b, size);
    else
        slob_free_pages(b, get_order(size));
}

static void kmem_rcu_free(struct rcu_head *head)
{
    struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
    void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));

    __kmem_cache_free(b, slob_rcu->size);
}

void kmem_cache_free(struct kmem_cache *c, void *b)
{
    kmemleak_free_recursive(b, c->flags);
    if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
        struct slob_rcu *slob_rcu;
        slob_rcu = b + (c->size - sizeof(struct slob_rcu));
        slob_rcu->size = c->size;
        call_rcu(&slob_rcu->head, kmem_rcu_free);
    } else {
        __kmem_cache_free(b, c->size);
    }

    trace_kmem_cache_free(_RET_IP_, b);
}
EXPORT_SYMBOL(kmem_cache_free);

unsigned int kmem_cache_size(struct kmem_cache *c)
{
    return c->size;
}
EXPORT_SYMBOL(kmem_cache_size);

int __kmem_cache_shutdown(struct kmem_cache *c)
{
    /* No way to check for remaining objects */
    return 0;
}

int kmem_cache_shrink(struct kmem_cache *d)
{
    return 0;
}
EXPORT_SYMBOL(kmem_cache_shrink);

struct kmem_cache kmem_cache_boot = {
    .name = "kmem_cache",
    .size = sizeof(struct kmem_cache),
    .flags = SLAB_PANIC,
    .align = ARCH_KMALLOC_MINALIGN,
};

void __init kmem_cache_init(void)
{
    kmem_cache = &kmem_cache_boot;
    slab_state = UP;
}

void __init kmem_cache_init_late(void)
{
    slab_state = FULL;
}