linux-kernel - [PATCH] memcg: remove trylock_page

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Date:	Wed, 22 Apr 2009 12:16:41 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	balbir@...ux.vnet.ibm.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: [PATCH] memcg: remove trylock_page_cgroup

How about this ? worth to be tested, I think.
-Kame
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Before synchronized-LRU patch, mem cgroup had its own LRU lock.
And there was a code which does
# assume mz as per zone struct of memcg. 

   spin_lock mz->lru_lock
	lock_page_cgroup(pc).
   and
   lock_page_cgroup(pc)
	spin_lock mz->lru_lock

because we cannot locate "mz" until we see pc->page_cgroup, we used
trylock(). But now, we don't have mz->lru_lock. All cgroup
uses zone->lru_lock for handling list. Moreover, manipulation of
LRU depends on global LRU now and we can isolate page from LRU by
very generic way.(isolate_lru_page()).
So, this kind of trylock is not necessary now.

I thought I removed all trylock in synchronized-LRU patch but there
is still one. This patch removes trylock used in memcontrol.c and
its definition. If someone needs, he should add this again with enough
reason.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
 include/linux/page_cgroup.h |    5 -----
 mm/memcontrol.c             |    3 +--
 2 files changed, 1 insertion(+), 7 deletions(-)

Index: mmotm-2.6.30-Apr21/include/linux/page_cgroup.h
===================================================================
--- mmotm-2.6.30-Apr21.orig/include/linux/page_cgroup.h
+++ mmotm-2.6.30-Apr21/include/linux/page_cgroup.h
@@ -61,11 +61,6 @@ static inline void lock_page_cgroup(stru
 	bit_spin_lock(PCG_LOCK, &pc->flags);
 }
 
-static inline int trylock_page_cgroup(struct page_cgroup *pc)
-{
-	return bit_spin_trylock(PCG_LOCK, &pc->flags);
-}
-
 static inline void unlock_page_cgroup(struct page_cgroup *pc)
 {
 	bit_spin_unlock(PCG_LOCK, &pc->flags);
Index: mmotm-2.6.30-Apr21/mm/memcontrol.c
===================================================================
--- mmotm-2.6.30-Apr21.orig/mm/memcontrol.c
+++ mmotm-2.6.30-Apr21/mm/memcontrol.c
@@ -1148,8 +1148,7 @@ static int mem_cgroup_move_account(struc
 	from_mz =  mem_cgroup_zoneinfo(from, nid, zid);
 	to_mz =  mem_cgroup_zoneinfo(to, nid, zid);
 
-	if (!trylock_page_cgroup(pc))
-		return ret;
+	lock_page_cgroup(pc);
 
 	if (!PageCgroupUsed(pc))
 		goto out;

--
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