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Message-Id: <20080514171301.99e5d55e.kamezawa.hiroyu@jp.fujitsu.com>
Date: Wed, 14 May 2008 17:13:01 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
"xemul@...nvz.org" <xemul@...nvz.org>,
"yamamoto@...inux.co.jp" <yamamoto@...inux.co.jp>,
"hugh@...itas.com" <hugh@...itas.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: [RFC/PATCH 6/6] memcg: remove redundant check at charge
Because of remove refcnt patch, it's very rare case to that
mem_cgroup_charge_common() is called against a page which is accounted.
mem_cgroup_charge_common() is called when.
1. a page is added into file cache.
2. an anon page is _newly_ mapped.
A racy case is that a newly-swapped-in anonymous page is referred from
prural threads in do_swap_page() at the same time.
(a page is not Locked when mem_cgroup_charge() is called from do_swap_page.)
Signed-off-by : KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
mm/memcontrol.c | 34 ++++------------------------------
1 file changed, 4 insertions(+), 30 deletions(-)
Index: linux-2.6.26-rc2/mm/memcontrol.c
===================================================================
--- linux-2.6.26-rc2.orig/mm/memcontrol.c
+++ linux-2.6.26-rc2/mm/memcontrol.c
@@ -536,28 +536,6 @@ static int mem_cgroup_charge_common(stru
if (mem_cgroup_subsys.disabled)
return 0;
- /*
- * Should page_cgroup's go to their own slab?
- * One could optimize the performance of the charging routine
- * by saving a bit in the page_flags and using it as a lock
- * to see if the cgroup page already has a page_cgroup associated
- * with it
- */
-retry:
- lock_page_cgroup(page);
- pc = page_get_page_cgroup(page);
- /*
- * The page_cgroup exists and
- * the page has already been accounted.
- */
- if (unlikely(pc)) {
- VM_BUG_ON(pc->page != page);
- VM_BUG_ON(!pc->mem_cgroup);
- unlock_page_cgroup(page);
- goto done;
- }
- unlock_page_cgroup(page);
-
pc = kmem_cache_alloc(page_cgroup_cache, gfp_mask);
if (unlikely(pc == NULL))
goto err;
@@ -618,15 +596,10 @@ retry:
lock_page_cgroup(page);
if (unlikely(page_get_page_cgroup(page))) {
unlock_page_cgroup(page);
- /*
- * Another charge has been added to this page already.
- * We take lock_page_cgroup(page) again and read
- * page->cgroup, increment refcnt.... just retry is OK.
- */
res_counter_uncharge(&mem->res, PAGE_SIZE);
css_put(&mem->css);
kmem_cache_free(page_cgroup_cache, pc);
- goto retry;
+ goto done;
}
page_assign_page_cgroup(page, pc);
--
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