On Sat, Oct 20, 2012 at 6:48 PM, Joonsoo Kim <js1304@xxxxxxxxx> 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@xxxxxxxxx>
> Signed-off-by: Joonsoo Kim <js1304@xxxxxxxxx>
> ---
> 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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