linux-kernel - [PATCH v2 01/10] slab: add unlikely macro to help compiler

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Message-Id: <1399442780-28748-2-git-send-email-iamjoonsoo.kim@lge.com>
Date:	Wed,  7 May 2014 15:06:11 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <js1304@...il.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: [PATCH v2 01/10] slab: add unlikely macro to help compiler

slab_should_failslab() is called on every allocation, so to optimize it
is reasonable. We normally don't allocate from kmem_cache. It is just
used when new kmem_cache is created, so it's very rare case. Therefore,
add unlikely macro to help compiler optimization.

Acked-by: David Rientjes <rientjes@...gle.com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

diff --git a/mm/slab.c b/mm/slab.c
index 25317fd..1fede40 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2993,7 +2993,7 @@ static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep,
 
 static bool slab_should_failslab(struct kmem_cache *cachep, gfp_t flags)
 {
-	if (cachep == kmem_cache)
+	if (unlikely(cachep == kmem_cache))
 		return false;
 
 	return should_failslab(cachep->object_size, flags, cachep->flags);
-- 
1.7.9.5

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