[PATCH] slab: Bypass free lists for __drain_alien_cache()

__drain_alien_cache() currently drains objects by freeing them to the
(remote) freelists of the original node.  However, each node also has a
shared list containing objects to be used on any processor of that node.
We can avoid a number of remote node accesses by copying the pointers to
the free objects directly into the remote shared array.

And while we are at it: Skip alien draining if the alien cache spinlock is
already taken.

Kiran reported that this is a performance benefit.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/mm/slab.c b/mm/slab.c
index dee857a8680b..351aa6c587f7 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -971,6 +971,13 @@ static void __drain_alien_cache(struct kmem_cache *cachep,
 
         if (ac->avail) {
                 spin_lock(&rl3->list_lock);
+                /*
+                 * Stuff objects into the remote nodes shared array first.
+                 * That way we could avoid the overhead of putting the objects
+                 * into the free lists and getting them back later.
+                 */
+                transfer_objects(rl3->shared, ac, ac->limit);
+
                 free_block(cachep, ac->entry, ac->avail, node);
                 ac->avail = 0;
                 spin_unlock(&rl3->list_lock);
@@ -986,8 +993,8 @@ static void reap_alien(struct kmem_cache *cachep, struct kmem_list3 *l3)
 
         if (l3->alien) {
                 struct array_cache *ac = l3->alien[node];
-                if (ac && ac->avail) {
-                        spin_lock_irq(&ac->lock);
+
+                if (ac && ac->avail && spin_trylock_irq(&ac->lock)) {
                         __drain_alien_cache(cachep, ac, node);
                         spin_unlock_irq(&ac->lock);
                 }