Commit 692e7c45 authored Aug 06, 2014 by Johannes Weiner Committed by Linus Torvalds Aug 06, 2014

mm: memcontrol: catch root bypass in move precharge



When mem_cgroup_try_charge() returns -EINTR, it bypassed the charge to
the root memcg.  But move precharging does not catch this and treats
this case as if no charge had happened, thus leaking a charge against
root.  Because of an old optimization, the root memcg's res_counter is
not actually charged right now, but it's still an imbalance and
subsequent patches will charge the root memcg again.

Catch those bypasses to the root memcg and properly cancel them before
giving up the move.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 9476db97

mm/memcontrol.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -6401,6 +6401,10 @@ static int mem_cgroup_do_precharge(unsigned long count)
		mc.precharge += count;
		return ret;
		}
		if (ret == -EINTR) {
		__mem_cgroup_cancel_charge(root_mem_cgroup, count);
		return ret;
		}

		/* Try charges one by one with reclaim */
		while (count--) {
		@@ -6409,8 +6413,11 @@ static int mem_cgroup_do_precharge(unsigned long count)
		/*
		* In case of failure, any residual charges against
		* mc.to will be dropped by mem_cgroup_clear_mc()
		* later on.
		* later on. However, cancel any charges that are
		* bypassed to root right away or they'll be lost.
		*/
		if (ret == -EINTR)
		__mem_cgroup_cancel_charge(root_mem_cgroup, 1);
		if (ret)
		return ret;
		mc.precharge++;

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