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Subject[PATCH] memcg: remove trylock_page_cgroup
How about this ? worth to be tested, I think.
-Kame
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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@jp.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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