From 8a9c61d4381c5e5007cc68e023940b18fa0808d7 Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Wed, 6 Aug 2014 16:04:20 -0700 Subject: slab: add unlikely macro to help compiler This patchset does some cleanup and tries to remove lockdep annotation. Patches 1~2 are just for really really minor improvement. Patches 3~9 are for clean-up and removing lockdep annotation. There are two cases that lockdep annotation is needed in SLAB. 1) holding two node locks 2) holding two array cache(alien cache) locks I looked at the code and found that we can avoid these cases without any negative effect. 1) occurs if freeing object makes new free slab and we decide to destroy it. Although we don't need to hold the lock during destroying a slab, current code do that. Destroying a slab without holding the lock would help the reduction of the lock contention. To do it, I change the implementation that new free slab is destroyed after releasing the lock. 2) occurs on similar situation. When we free object from non-local node, we put this object to alien cache with holding the alien cache lock. If alien cache is full, we try to flush alien cache to proper node cache, and, in this time, new free slab could be made. Destroying it would be started and we will free metadata object which comes from another node. In this case, we need another node's alien cache lock to free object. This forces us to hold two array cache locks and then we need lockdep annotation although they are always different locks and deadlock cannot be possible. To prevent this situation, I use same way as 1). In this way, we can avoid 1) and 2) cases, and then, can remove lockdep annotation. As short stat noted, this makes SLAB code much simpler. This patch (of 9): 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. Signed-off-by: Joonsoo Kim Acked-by: David Rientjes Acked-by: Christoph Lameter Cc: Pekka Enberg Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/slab.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'mm/slab.c') diff --git a/mm/slab.c b/mm/slab.c index 66b3ffbb890d..7d07942b9804 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3048,7 +3048,7 @@ 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); -- cgit v1.2.3-70-g09d2