[PATCH] slub: reduce duplicate creation on the first object

[Wei Yang]

When a kmem_cache is created with ctor, each object in the kmem_cache will be
initialized before ready to use. While in slub implementation, the first
object will be initialized twice.

This patch reduces the duplication of initialization of the first object.

Fix commit 7656c72b: SLUB: add macros for scanning objects in a slab.

Signed-off-by: Wei Yang <weiyang@xxxxxxxxxxxxxxxxxx>
---
 mm/slub.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index b2b0473..79611d9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -288,6 +288,10 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
 	for (__p = (__addr); __p < (__addr) + (__objects) * (__s)->size;\
 			__p += (__s)->size)
 
+#define for_each_object_idx(__p, __idx, __s, __addr, __objects) \
+	for (__p = (__addr), __idx = 1; __idx <= __objects;\
+			__p += (__s)->size, __idx++)
+
 /* Determine object index from a given position */
 static inline int slab_index(void *p, struct kmem_cache *s, void *addr)
 {
@@ -1409,9 +1413,9 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
 {
 	struct page *page;
 	void *start;
-	void *last;
 	void *p;
 	int order;
+	int idx;
 
 	BUG_ON(flags & GFP_SLAB_BUG_MASK);
 
@@ -1432,14 +1436,13 @@ static struct page *new_slab(struct kmem_cache *s, gfp_t flags, int node)
 	if (unlikely(s->flags & SLAB_POISON))
 		memset(start, POISON_INUSE, PAGE_SIZE << order);
 
-	last = start;
-	for_each_object(p, s, start, page->objects) {
-		setup_object(s, page, last);
-		set_freepointer(s, last, p);
-		last = p;
+	for_each_object_idx(p, idx, s, start, page->objects) {
+		setup_object(s, page, p);
+		if (likely(idx < page->objects))
+			set_freepointer(s, p, p + s->size);
+		else
+			set_freepointer(s, p, NULL);
 	}
-	setup_object(s, page, last);
-	set_freepointer(s, last, NULL);
 
 	page->freelist = start;
 	page->inuse = page->objects;
-- 
1.7.9.5


-- 
Richard Yang
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