[RFC][PATCH 2/2] memcg: coalescing css_put

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>]

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

memory cgroup adds a css-refcnt per a page and we decrement it at
uncharge(). Now, we do uncharge in batch if possible. So, css_put()
can be called in batch.

This patch reduces the call of atomic_dec() and make memcg faster
on smp system. And we need small modification for SWAPOUT routine.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
 mm/memcontrol.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

Index: mmotm-2.6.34-May21/mm/memcontrol.c
===================================================================
--- mmotm-2.6.34-May21.orig/mm/memcontrol.c
+++ mmotm-2.6.34-May21/mm/memcontrol.c
@@ -2304,6 +2304,7 @@ direct_uncharge:
 		res_counter_uncharge(&mem->memsw, PAGE_SIZE);
 	if (unlikely(batch->memcg != mem))
 		memcg_oom_recover(mem);
+	css_put(&mem->css);
 	return;
 }
 
@@ -2373,9 +2374,6 @@ __mem_cgroup_uncharge_common(struct page
 	unlock_page_cgroup(pc);
 
 	memcg_check_events(mem, page);
-	/* at swapout, this memcg will be accessed to record to swap */
-	if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
-		css_put(&mem->css);
 
 	return mem;
 
@@ -2441,6 +2439,7 @@ void mem_cgroup_uncharge_end(void)
 		res_counter_uncharge(&batch->memcg->res, batch->bytes);
 	if (batch->memsw_bytes)
 		res_counter_uncharge(&batch->memcg->memsw, batch->memsw_bytes);
+	__css_put(&batch->memcg->css, batch->bytes/PAGE_SIZE);
 	memcg_oom_recover(batch->memcg);
 	/* forget this pointer (for sanity check) */
 	batch->memcg = NULL;
@@ -2456,19 +2455,22 @@ mem_cgroup_uncharge_swapcache(struct pag
 {
 	struct mem_cgroup *memcg;
 	int ctype = MEM_CGROUP_CHARGE_TYPE_SWAPOUT;
+	struct mem_cgroup *keep = NULL;
 
 	if (!swapout) /* this was a swap cache but the swap is unused ! */
 		ctype = MEM_CGROUP_CHARGE_TYPE_DROP;
+	else
+		keep = try_get_mem_cgroup_from_page(page);
 
 	memcg = __mem_cgroup_uncharge_common(page, ctype);
 
 	/* record memcg information */
-	if (do_swap_account && swapout && memcg) {
+	if (do_swap_account && swapout && memcg && keep == memcg) {
 		swap_cgroup_record(ent, css_id(&memcg->css));
 		mem_cgroup_get(memcg);
 	}
-	if (swapout && memcg)
-		css_put(&memcg->css);
+	if (keep)
+		css_put(&keep->css);
 }
 #endif
 

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