From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 080/155] mm: memcg: make memory.oom.group tolerable to task migration Date: Wed, 01 Apr 2020 21:07:39 -0700 Message-ID: <20200402040739.PB5HXuW7o%akpm@linux-foundation.org> References: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:58900 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726963AbgDBEHk (ORCPT ); Thu, 2 Apr 2020 00:07:40 -0400 In-Reply-To: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, dschatzberg@fb.com, guro@fb.com, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@suse.com, mm-commits@vger.kernel.org, torvalds@linux-foundation.org From: Roman Gushchin Subject: mm: memcg: make memory.oom.group tolerable to task migration If a task is getting moved out of the OOMing cgroup, it might result in unexpected OOM killings if memory.oom.group is used anywhere in the cgroup tree. Imagine the following example: A (oom.group = 1) / \ (OOM) B C Let's say B's memory.max is exceeded and it's OOMing. The OOM killer selects a task in B as a victim, but someone asynchronously moves the task into C. mem_cgroup_get_oom_group() will iterate over all ancestors of C up to the root cgroup. In theory it had to stop at the oom_domain level - the memory cgroup which is OOMing. But because B is not an ancestor of C, it's not happening. Instead it chooses A (because it's oom.group is set), and kills all tasks in A. This behavior is wrong because the OOM happened in B, so there is no reason to kill anything outside. Fix this by checking it the memory cgroup to which the task belongs is a descendant of the oom_domain. If not, memory.oom.group should be ignored, and the OOM killer should kill only the victim task. Link: http://lkml.kernel.org/r/20200316223510.3176148-1-guro@fb.com Signed-off-by: Roman Gushchin Reported-by: Dan Schatzberg Acked-by: Michal Hocko Acked-by: Johannes Weiner Signed-off-by: Andrew Morton --- mm/memcontrol.c | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/mm/memcontrol.c~mm-memcg-make-memoryoomgroup-tolerable-to-task-migration +++ a/mm/memcontrol.c @@ -1931,6 +1931,14 @@ struct mem_cgroup *mem_cgroup_get_oom_gr goto out; /* + * If the victim task has been asynchronously moved to a different + * memory cgroup, we might end up killing tasks outside oom_domain. + * In this case it's better to ignore memory.group.oom. + */ + if (unlikely(!mem_cgroup_is_descendant(memcg, oom_domain))) + goto out; + + /* * Traverse the memory cgroup hierarchy from the victim task's * cgroup up to the OOMing cgroup (or root) to find the * highest-level memory cgroup with oom.group set. _