On Thu, Nov 12, 2015 at 06:41:22PM -0500, Johannes Weiner wrote:

When charging socket memory, the code currently checks only the local
page counter for excess to determine whether the memcg is under socket
pressure. But even if the local counter is fine, one of the ancestors
could have breached its limit, which should also force this child to
enter socket pressure. This currently doesn't happen.

Fix this by using page_counter_try_charge() first. If that fails, it
means that either the local counter or one of the ancestors are in
excess of their limit, and the child should enter socket pressure.

Signed-off-by: Johannes Weiner <redacted>

Reviewed-by: Vladimir Davydov <redacted>

For the record: it was broken by commit 3e32cb2e0a12 ("mm: memcontrol:
lockless page counters").