memcg: add lock to synchronize page accounting and migration

Introduce a new bit spin lock, PCG_MOVE_LOCK, to synchronize the page
accounting and migration code.  This reworks the locking scheme of
_update_stat() and _move_account() by adding new lock bit PCG_MOVE_LOCK,
which is always taken under IRQ disable.

1. If pages are being migrated from a memcg, then updates to that
   memcg page statistics are protected by grabbing PCG_MOVE_LOCK using
   move_lock_page_cgroup().  In an upcoming commit, memcg dirty page
   accounting will be updating memcg page accounting (specifically: num
   writeback pages) from IRQ context (softirq).  Avoid a deadlocking
   nested spin lock attempt by disabling irq on the local processor when
   grabbing the PCG_MOVE_LOCK.

2. lock for update_page_stat is used only for avoiding race with
   move_account().  So, IRQ awareness of lock_page_cgroup() itself is not
   a problem.  The problem is between mem_cgroup_update_page_stat() and
   mem_cgroup_move_account_page().

Trade-off:
  * Changing lock_page_cgroup() to always disable IRQ (or
    local_bh) has some impacts on performance and I think
    it's bad to disable IRQ when it's not necessary.
  * adding a new lock makes move_account() slower.  Score is
    here.

Performance Impact: moving a 8G anon process.

Before:
	real    0m0.792s
	user    0m0.000s
	sys     0m0.780s

After:
	real    0m0.854s
	user    0m0.000s
	sys     0m0.842s

This score is bad but planned patches for optimization can reduce
this impact.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Greg Thelen <gthelen@google.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Andrea Righi <arighi@develer.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3d8a0c7..d888956 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1606,6 +1606,7 @@ void mem_cgroup_update_page_stat(struct page *page,
 	struct mem_cgroup *mem;
 	struct page_cgroup *pc = lookup_page_cgroup(page);
 	bool need_unlock = false;
+	unsigned long uninitialized_var(flags);
 
 	if (unlikely(!pc))
 		return;
@@ -1617,7 +1618,7 @@ void mem_cgroup_update_page_stat(struct page *page,
 	/* pc->mem_cgroup is unstable ? */
 	if (unlikely(mem_cgroup_stealed(mem))) {
 		/* take a lock against to access pc->mem_cgroup */
-		lock_page_cgroup(pc);
+		move_lock_page_cgroup(pc, &flags);
 		need_unlock = true;
 		mem = pc->mem_cgroup;
 		if (!mem || !PageCgroupUsed(pc))
@@ -1640,7 +1641,7 @@ void mem_cgroup_update_page_stat(struct page *page,
 
 out:
 	if (unlikely(need_unlock))
-		unlock_page_cgroup(pc);
+		move_unlock_page_cgroup(pc, &flags);
 	rcu_read_unlock();
 	return;
 }
@@ -2211,9 +2212,13 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
 		struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
 {
 	int ret = -EINVAL;
+	unsigned long flags;
+
 	lock_page_cgroup(pc);
 	if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
+		move_lock_page_cgroup(pc, &flags);
 		__mem_cgroup_move_account(pc, from, to, uncharge);
+		move_unlock_page_cgroup(pc, &flags);
 		ret = 0;
 	}
 	unlock_page_cgroup(pc);