slab: shrink sizeof(struct kmem_cache)

Reduce high order allocations for some setups.
(NR_CPUS=4096 -> we need 64KB per kmem_cache struct)

We now allocate exact needed size (using nr_cpu_ids and nr_node_ids)

This also makes code a bit smaller on x86_64, since some field offsets
are less than the 127 limit :

Before patch :
# size mm/slab.o
   text    data     bss     dec     hex filename
  22605  361665      32  384302   5dd2e mm/slab.o

After patch :
# size mm/slab.o
   text    data     bss     dec     hex filename
  22349	 353473	   8224	 384046	  5dc2e	mm/slab.o

CC: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/mm/slab.c b/mm/slab.c
index ef8ceb726e71..c3cb3598555a 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -574,7 +574,9 @@ static struct arraycache_init initarray_generic =
     { {0, BOOT_CPUCACHE_ENTRIES, 1, 0} };
 
 /* internal cache of cache description objs */
+static struct kmem_list3 *cache_cache_nodelists[MAX_NUMNODES];
 static struct kmem_cache cache_cache = {
+        .nodelists = cache_cache_nodelists,
         .batchcount = 1,
         .limit = BOOT_CPUCACHE_ENTRIES,
         .shared = 1,
@@ -1492,11 +1494,10 @@ void __init kmem_cache_init(void)
         cache_cache.nodelists[node] = &initkmem_list3[CACHE_CACHE + node];
 
         /*
-         * struct kmem_cache size depends on nr_node_ids, which
-         * can be less than MAX_NUMNODES.
+         * struct kmem_cache size depends on nr_node_ids & nr_cpu_ids
          */
-        cache_cache.buffer_size = offsetof(struct kmem_cache, nodelists) +
-                                 nr_node_ids * sizeof(struct kmem_list3 *);
+        cache_cache.buffer_size = offsetof(struct kmem_cache, array[nr_cpu_ids]) +
+                                  nr_node_ids * sizeof(struct kmem_list3 *);
 #if DEBUG
         cache_cache.obj_size = cache_cache.buffer_size;
 #endif
@@ -2308,6 +2309,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
         if (!cachep)
                 goto oops;
 
+        cachep->nodelists = (struct kmem_list3 **)&cachep->array[nr_cpu_ids];
 #if DEBUG
         cachep->obj_size = size;