Re: [rfc 04/18] slub: Use freelist instead of "object" in __slab_alloc

[Pekka Enberg <penberg@kernel.org>]

On Fri, Nov 11, 2011 at 10:07 PM, Christoph Lameter <cl@linux.com> wrote:
> The variable "object" really refers to a list of objects that we
> are handling. Since the lockless allocator path will depend on it
> we rename the variable now.
>
> Signed-off-by: Christoph Lameter <cl@linux.com>

Also a reasonable cleanup.

> ---
>  mm/slub.c |   40 ++++++++++++++++++++++------------------
>  1 file changed, 22 insertions(+), 18 deletions(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c    2011-11-09 11:11:13.471490305 -0600
> +++ linux-2.6/mm/slub.c 2011-11-09 11:11:22.381541568 -0600
> @@ -2084,7 +2084,7 @@ slab_out_of_memory(struct kmem_cache *s,
>  static inline void *new_slab_objects(struct kmem_cache *s, gfp_t flags,
>                        int node, struct kmem_cache_cpu **pc)
>  {
> -       void *object;
> +       void *freelist;
>        struct kmem_cache_cpu *c;
>        struct page *page = new_slab(s, flags, node);
>
> @@ -2097,16 +2097,16 @@ static inline void *new_slab_objects(str
>                 * No other reference to the page yet so we can
>                 * muck around with it freely without cmpxchg
>                 */
> -               object = page->freelist;
> +               freelist = page->freelist;
>                page->freelist = NULL;
>
>                stat(s, ALLOC_SLAB);
>                c->page = page;
>                *pc = c;
>        } else
> -               object = NULL;
> +               freelist = NULL;
>
> -       return object;
> +       return freelist;
>  }
>
>  /*
> @@ -2159,7 +2159,7 @@ static inline void *get_freelist(struct
>  static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
>                          unsigned long addr, struct kmem_cache_cpu *c)
>  {
> -       void **object;
> +       void *freelist;
>        unsigned long flags;
>
>        local_irq_save(flags);
> @@ -2175,6 +2175,7 @@ static void *__slab_alloc(struct kmem_ca
>        if (!c->page)
>                goto new_slab;
>  redo:
> +
>        if (unlikely(!node_match(c, node))) {
>                stat(s, ALLOC_NODE_MISMATCH);
>                deactivate_slab(s, c->page, c->freelist);
> @@ -2185,9 +2186,9 @@ redo:
>
>        stat(s, ALLOC_SLOWPATH);
>
> -       object = get_freelist(s, c->page);
> +       freelist = get_freelist(s, c->page);
>
> -       if (!object) {
> +       if (unlikely(!freelist)) {
>                c->page = NULL;
>                stat(s, DEACTIVATE_BYPASS);
>                goto new_slab;
> @@ -2196,10 +2197,15 @@ redo:
>        stat(s, ALLOC_REFILL);
>
>  load_freelist:
> -       c->freelist = get_freepointer(s, object);
> +       /*
> +        * freelist is pointing to the list of objects to be used.
> +        * page is pointing to the page from which the objects are obtained.
> +        */
> +       VM_BUG_ON(!c->page->frozen);
> +       c->freelist = get_freepointer(s, freelist);
>        c->tid = next_tid(c->tid);
>        local_irq_restore(flags);
> -       return object;
> +       return freelist;
>
>  new_slab:
>
> @@ -2211,14 +2217,12 @@ new_slab:
>                goto redo;
>        }
>
> -       /* Then do expensive stuff like retrieving pages from the partial lists */
> -       object = get_partial(s, gfpflags, node, c);
> +       freelist = get_partial(s, gfpflags, node, c);
>
> -       if (unlikely(!object)) {
> +       if (unlikely(!freelist)) {
> +               freelist = new_slab_objects(s, gfpflags, node, &c);
>
> -               object = new_slab_objects(s, gfpflags, node, &c);
> -
> -               if (unlikely(!object)) {
> +               if (unlikely(!freelist)) {
>                        if (!(gfpflags & __GFP_NOWARN) && printk_ratelimit())
>                                slab_out_of_memory(s, gfpflags, node);
>
> @@ -2231,14 +2235,14 @@ new_slab:
>                goto load_freelist;
>
>        /* Only entered in the debug case */
> -       if (!alloc_debug_processing(s, c->page, object, addr))
> +       if (!alloc_debug_processing(s, c->page, freelist, addr))
>                goto new_slab;  /* Slab failed checks. Next slab needed */
> +       deactivate_slab(s, c->page, get_freepointer(s, freelist));
>
> -       deactivate_slab(s, c->page, get_freepointer(s, object));
>        c->page = NULL;
>        c->freelist = NULL;
>        local_irq_restore(flags);
> -       return object;
> +       return freelist;
>  }
>
>  /*
>
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