memcg: cleanup mem_cgroup_move_parent()

mem_cgroup_move_parent() calls try_charge first and cancel_charge on
failure.  IMHO, charge/uncharge(especially charge) is high cost operation,
so we should avoid it as far as possible.

This patch tries to delay try_charge in mem_cgroup_move_parent() by
re-ordering checks it does.

And this patch renames mem_cgroup_move_account() to
__mem_cgroup_move_account(), changes the return value of
__mem_cgroup_move_account() from int to void, and adds a new
wrapper(mem_cgroup_move_account()), which checks whether a @pc is valid
for moving account and calls __mem_cgroup_move_account().

This patch removes the last caller of trylock_page_cgroup(), so removes
its definition too.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 5 deletions

diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 4b938d4f3ac2..b0e4eb126236 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -57,6 +57,8 @@ static inline void ClearPageCgroup##uname(struct page_cgroup *pc)	\
 static inline int TestClearPageCgroup##uname(struct page_cgroup *pc)    \
         { return test_and_clear_bit(PCG_##lname, &pc->flags);  }
 
+TESTPCGFLAG(Locked, LOCK)
+
 /* Cache flag is set only once (at allocation) */
 TESTPCGFLAG(Cache, CACHE)
 CLEARPCGFLAG(Cache, CACHE)
@@ -86,11 +88,6 @@ static inline void lock_page_cgroup(struct page_cgroup *pc)
         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);