linux-kernel - [PATCH for-v3.7 1/2] slub: optimize poorly inlined kmalloc* functions

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Date:	Sun, 21 Oct 2012 00:48:12 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Joonsoo Kim <js1304@...il.com>,
	Christoph Lameter <cl@...ux.com>
Subject: [PATCH for-v3.7 1/2] slub: optimize poorly inlined kmalloc* functions

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@...ux.com>
Signed-off-by: Joonsoo Kim <js1304@...il.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

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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