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    Subject[PATCH 4/8] Cleanup kmem_cache_create()
    Cleanup kmem_cache_create()

    mcd@arrakis:~/linux/source/linux-2.6.14+slab_cleanup/patches $ diffstat
    kmem_cache_create.patch
    slab.c | 69
    ++++++++++++++++++++++++++++-------------------------------------
    1 files changed, 30 insertions(+), 39 deletions(-)

    -Matt

    General readability fixes.

    * Reformat a looong if statement
    * Replace a constant (4096) with what it represents (PAGE_SIZE)
    * Replace a confusing label (opps) with a more sensible one (out)
    * Refactor a do {} while loop w/ a couple labels and gotos into
    a for loop with breaks and continues.
    * Rewrite some confusing slab alignment code for readability
    * Replace a list_for_each/list_entry combo with an identical but
    more readable list_for_each_entry loop.

    Index: linux-2.6.14+slab_cleanup/mm/slab.c
    ===================================================================
    --- linux-2.6.14+slab_cleanup.orig/mm/slab.c 2005-11-07 15:58:48.547771048 -0800
    +++ linux-2.6.14+slab_cleanup/mm/slab.c 2005-11-07 15:58:50.495474952 -0800
    @@ -1499,21 +1499,18 @@ kmem_cache_t *kmem_cache_create(const ch
    void (*ctor)(void *, kmem_cache_t *, unsigned long),
    void (*dtor)(void *, kmem_cache_t *, unsigned long))
    {
    - size_t left_over, slab_size, ralign;
    + size_t left_over, slab_size, aligned_slab_size, ralign;
    kmem_cache_t *cachep = NULL;

    /*
    * Sanity checks... these are all serious usage bugs.
    */
    - if ((!name) ||
    - in_interrupt() ||
    - (size < BYTES_PER_WORD) ||
    - (size > (1<<MAX_OBJ_ORDER)*PAGE_SIZE) ||
    - (dtor && !ctor)) {
    - printk(KERN_ERR "%s: Early error in slab %s\n",
    - __FUNCTION__, name);
    - BUG();
    - }
    + if (!name || in_interrupt() || (size < BYTES_PER_WORD) ||
    + (size > (1 << MAX_OBJ_ORDER) * PAGE_SIZE) || (dtor && !ctor)) {
    + printk(KERN_ERR "%s: Early error in slab %s\n",
    + __FUNCTION__, name);
    + BUG();
    + }

    #if DEBUG
    WARN_ON(strchr(name, ' ')); /* It confuses parsers */
    @@ -1531,7 +1528,7 @@ kmem_cache_t *kmem_cache_create(const ch
    * above the next power of two: caches with object sizes just above a
    * power of two have a significant amount of internal fragmentation.
    */
    - if ((size < 4096 || fls(size-1) == fls(size-1+3*BYTES_PER_WORD)))
    + if (size < PAGE_SIZE || fls(size-1) == fls(size-1 + 3*BYTES_PER_WORD))
    flags |= SLAB_RED_ZONE|SLAB_STORE_USER;
    if (!(flags & SLAB_DESTROY_BY_RCU))
    flags |= SLAB_POISON;
    @@ -1594,7 +1591,7 @@ kmem_cache_t *kmem_cache_create(const ch
    /* Get cache's description obj. */
    cachep = (kmem_cache_t *) kmem_cache_alloc(&cache_cache, SLAB_KERNEL);
    if (!cachep)
    - goto opps;
    + goto out;
    memset(cachep, 0, sizeof(kmem_cache_t));

    #if DEBUG
    @@ -1652,9 +1649,9 @@ kmem_cache_t *kmem_cache_create(const ch
    * gfp() funcs are more friendly towards high-order requests,
    * this should be changed.
    */
    - do {
    - unsigned int break_flag = 0;
    -cal_wastage:
    + unsigned int break_flag = 0;
    +
    + for ( ; ; cachep->gfporder++) {
    cache_estimate(cachep->gfporder, size, align, flags,
    &left_over, &cachep->num);
    if (break_flag)
    @@ -1662,13 +1659,13 @@ cal_wastage:
    if (cachep->gfporder >= MAX_GFP_ORDER)
    break;
    if (!cachep->num)
    - goto next;
    - if (flags & CFLGS_OFF_SLAB &&
    - cachep->num > offslab_limit) {
    + continue;
    + if ((flags & CFLGS_OFF_SLAB) &&
    + (cachep->num > offslab_limit)) {
    /* This num of objs will cause problems. */
    - cachep->gfporder--;
    + cachep->gfporder -= 2;
    break_flag++;
    - goto cal_wastage;
    + continue;
    }

    /*
    @@ -1680,33 +1677,29 @@ cal_wastage:

    if ((left_over*8) <= (PAGE_SIZE<<cachep->gfporder))
    break; /* Acceptable internal fragmentation. */
    -next:
    - cachep->gfporder++;
    - } while (1);
    + }
    }

    if (!cachep->num) {
    printk("kmem_cache_create: couldn't create cache %s.\n", name);
    kmem_cache_free(&cache_cache, cachep);
    cachep = NULL;
    - goto opps;
    + goto out;
    }
    - slab_size = ALIGN(cachep->num*sizeof(kmem_bufctl_t)
    - + sizeof(struct slab), align);
    + slab_size = cachep->num * sizeof(kmem_bufctl_t) + sizeof(struct slab);
    + aligned_slab_size = ALIGN(slab_size, align);

    /*
    * If the slab has been placed off-slab, and we have enough space then
    * move it on-slab. This is at the expense of any extra colouring.
    */
    - if (flags & CFLGS_OFF_SLAB && left_over >= slab_size) {
    + if (flags & CFLGS_OFF_SLAB && left_over >= aligned_slab_size) {
    flags &= ~CFLGS_OFF_SLAB;
    - left_over -= slab_size;
    - }
    -
    - if (flags & CFLGS_OFF_SLAB) {
    - /* really off slab. No need for manual alignment */
    - slab_size = cachep->num*sizeof(kmem_bufctl_t)+sizeof(struct slab);
    + left_over -= aligned_slab_size;
    }
    + /* On slab, need manual alignment */
    + if (!(flags & CFLGS_OFF_SLAB))
    + slab_size = aligned_slab_size;

    cachep->colour_off = cache_line_size();
    /* Offset must be a multiple of the alignment. */
    @@ -1789,13 +1782,12 @@ next:
    /* Need the semaphore to access the chain. */
    down(&cache_chain_sem);
    {
    - struct list_head *p;
    + kmem_cache_t *pc;
    mm_segment_t old_fs;

    old_fs = get_fs();
    set_fs(KERNEL_DS);
    - list_for_each(p, &cache_chain) {
    - kmem_cache_t *pc = list_entry(p, kmem_cache_t, next);
    + list_for_each_entry(pc, &cache_chain, next) {
    char tmp;
    /*
    * This happens when the module gets unloaded & doesn't
    @@ -1821,10 +1813,9 @@ next:
    list_add(&cachep->next, &cache_chain);
    up(&cache_chain_sem);
    unlock_cpu_hotplug();
    -opps:
    +out:
    if (!cachep && (flags & SLAB_PANIC))
    - panic("kmem_cache_create(): failed to create slab `%s'\n",
    - name);
    + panic("%s: failed to create slab `%s'\n", __FUNCTION__, name);
    return cachep;
    }
    EXPORT_SYMBOL(kmem_cache_create);
    \
     
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      Last update: 2005-11-08 01:55    [W:4.539 / U:0.060 seconds]
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