On 02/03/2012 11:27 PM, Christoph Lameter wrote:

On Fri, 3 Feb 2012, Alex,Shi wrote:

quoted

This patch split the cpu_partial_free into 2 parts: cpu_partial_node, PCP refilling
times from node partial; and same name cpu_partial_free, PCP refilling times in
slab_free slow path. A new statistic 'release_cpu_partial' is added to get PCP
release times. These info are useful when do PCP tunning.

Releasing? The code where you inserted the new statistics counts the pages
put on the cpu partial list when refilling from the node partial list.

Ops, are we talking the same base kernel: Linus' tree?  :)
Here the Releasing code only be called in slow free path and the PCP is
full at the same time, not in PCP refilling from node partial.

explanations more below.

See more below.

quoted

 struct kmem_cache_cpu {

diff --git a/mm/slub.c b/mm/slub.c
index 4907563..5dd299c 100644
--- a/mm/slub.c
+++ b/mm/slub.c

@@ -1560,6 +1560,7 @@ static void *get_partial_node(struct kmem_cache *s,
 		} else {
 			page->freelist = t;
 			available = put_cpu_partial(s, page, 0);
+			stat(s, CPU_PARTIAL_NODE);

This is refilling the per cpu partial list from the node list.

Yes. and same as my explanation in patch:
-       CPU_PARTIAL_FREE,       /* USed cpu partial on free */
+       CPU_PARTIAL_FREE,       /* Refill cpu partial on free */
+       CPU_PARTIAL_NODE,       /* Refill cpu partial from node partial */

quoted

 		}
 		if (kmem_cache_debug(s) || available > s->cpu_partial / 2)
 			break;

@@ -1973,6 +1974,7 @@ int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)
 				local_irq_restore(flags);
 				pobjects = 0;
 				pages = 0;
+				stat(s, RELEASE_CPU_PARTIAL);

The callers count the cpu partial operations. Why is there now one in
put_cpu_partial? It is moving a page to the cpu partial list. Not
releasing it from the cpu partial list.

All old PCP will drain out on running CPU by unfreeze_partials() even it
is not accurate here. The new one is not lost counting. It still be
counted as CPU_PARTIAL_FREE in the following change as before.

If release is right, maybe named as drain_cpu_partial or
unfreeze_cpu_partial?

quoted

@@ -2465,9 +2466,10 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
 		 * If we just froze the page then put it onto the
 		 * per cpu partial list.
 		 */
-		if (new.frozen && !was_frozen)
+		if (new.frozen && !was_frozen) {
 			put_cpu_partial(s, page, 1);
-
+			stat(s, CPU_PARTIAL_FREE);

cpu partial list filled with a partial page created from a fully allocated
slab (which therefore was not on any list before).

Yes, but the counting is not new here. It just moved out of
put_cpu_partial().

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