SLAB: don't allocate empty shared caches

We can avoid allocating empty shared caches and avoid unecessary check of
cache->limit.  We save some memory.  We avoid bringing into CPU cache
unecessary cache lines.

All accesses to l3->shared are already checking NULL pointers so this patch is
safe.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Christoph Lameter <clameter@engr.sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 11 deletions

diff --git a/mm/slab.c b/mm/slab.c
index ae440b5ba60e..00f98b9f6df1 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1223,19 +1223,20 @@ static int __cpuinit cpuup_callback(struct notifier_block *nfb,
                  */
                 list_for_each_entry(cachep, &cache_chain, next) {
                         struct array_cache *nc;
-                        struct array_cache *shared;
+                        struct array_cache *shared = NULL;
                         struct array_cache **alien = NULL;
 
                         nc = alloc_arraycache(node, cachep->limit,
                                                 cachep->batchcount);
                         if (!nc)
                                 goto bad;
-                        shared = alloc_arraycache(node,
+                        if (cachep->shared) {
+                                shared = alloc_arraycache(node,
                                         cachep->shared * cachep->batchcount,
                                         0xbaadf00d);
-                        if (!shared)
-                                goto bad;
-
+                                if (!shared)
+                                        goto bad;
+                        }
                         if (use_alien_caches) {
                                 alien = alloc_alien_cache(node, cachep->limit);
                                 if (!alien)
@@ -1317,8 +1318,8 @@ static int __cpuinit cpuup_callback(struct notifier_block *nfb,
 
                         shared = l3->shared;
                         if (shared) {
-                                free_block(cachep, l3->shared->entry,
-                                           l3->shared->avail, node);
+                                free_block(cachep, shared->entry,
+                                           shared->avail, node);
                                 l3->shared = NULL;
                         }
 
@@ -3870,12 +3871,15 @@ static int alloc_kmemlist(struct kmem_cache *cachep)
                                 goto fail;
                 }
 
-                new_shared = alloc_arraycache(node,
+                new_shared = NULL;
+                if (cachep->shared) {
+                        new_shared = alloc_arraycache(node,
                                 cachep->shared*cachep->batchcount,
                                         0xbaadf00d);
-                if (!new_shared) {
-                        free_alien_cache(new_alien);
-                        goto fail;
+                        if (!new_shared) {
+                                free_alien_cache(new_alien);
+                                goto fail;
+                        }
                 }
 
                 l3 = cachep->nodelists[node];