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Subject: Re: [PATCH for-v3.7 1/2] slub: optimize poorly inlined kmalloc* functions
From: Pekka Enberg <penberg@kernel.org>
To: Joonsoo Kim <js1304@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Christoph Lameter <cl@linux.com>
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On Sat, Oct 20, 2012 at 6:48 PM, Joonsoo Kim <js1304@gmail.com> wrote:
> kmalloc() and kmalloc_node() is always inlined into generic code.
> However, there is a mistake in implemention of the SLUB.
>
> In kmalloc() and kmalloc_node() of the SLUB,
> we try to compare kmalloc_caches[index] with NULL.
> As it cannot be known at compile time,
> this comparison is inserted into generic code invoking kmalloc*.
> This may decrease system performance, so we should fix it.
>
> Below is the result of "size vmlinux"
> text size is decreased roughly 20KB
>
> Before:
>    text    data     bss     dec     hex filename
> 10044177        1443168 5722112 17209457        1069871 vmlinux
> After:
>    text    data     bss     dec     hex filename
> 10022627        1443136 5722112 17187875        1064423 vmlinux
>
> Cc: Christoph Lameter <cl@linux.com>
> Signed-off-by: Joonsoo Kim <js1304@gmail.com>
> ---
> With Christoph's patchset(common kmalloc caches:
> '[15/15] Common Kmalloc cache determination') which is not merged into mainline yet,
> this issue will be fixed.
> As it takes some time, I send this patch for v3.7
>
> This patch is based on v3.7-rc1

Looks reasonable to me. Christoph, any objections?

>
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index df448ad..4c75f2b 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -271,9 +271,10 @@ static __always_inline void *kmalloc(size_t size, gfp_t flags)
>                         return kmalloc_large(size, flags);
>
>                 if (!(flags & SLUB_DMA)) {
> -                       struct kmem_cache *s = kmalloc_slab(size);
> +                       int index = kmalloc_index(size);
> +                       struct kmem_cache *s = kmalloc_caches[index];
>
> -                       if (!s)
> +                       if (!index)
>                                 return ZERO_SIZE_PTR;
>
>                         return kmem_cache_alloc_trace(s, flags, size);
> @@ -304,9 +305,10 @@ static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
>  {
>         if (__builtin_constant_p(size) &&
>                 size <= SLUB_MAX_SIZE && !(flags & SLUB_DMA)) {
> -                       struct kmem_cache *s = kmalloc_slab(size);
> +               int index = kmalloc_index(size);
> +               struct kmem_cache *s = kmalloc_caches[index];
>
> -               if (!s)
> +               if (!index)
>                         return ZERO_SIZE_PTR;
>
>                 return kmem_cache_alloc_node_trace(s, flags, node, size);
> --
> 1.7.9.5
>
> --
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