From mboxrd@z Thu Jan 1 00:00:00 1970 From: linmiaohe Subject: Re: [PATCH v2] mm: memcontrol: remove obsolete comment of mem_cgroup_unmark_under_oom() Date: Wed, 30 Sep 2020 01:34:25 +0000 Message-ID: <7d1ea112d8a740cab555eaf7be530286@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT Return-path: Content-Language: zh-CN List-ID: To: Michal Hocko Cc: "hannes@cmpxchg.org" , "vdavydov.dev@gmail.com" , "akpm@linux-foundation.org" , "cgroups@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Michal Hocko wrote: > On Thu 17-09-20 06:59:00, Miaohe Lin wrote: >> Since commit 79dfdaccd1d5 ("memcg: make oom_lock 0 and 1 based rather >> than counter"), the mem_cgroup_unmark_under_oom() is added and the >> comment of the mem_cgroup_oom_unlock() is moved here. But this comment >> make no sense here because mem_cgroup_oom_lock() does not operate on under_oom field. > >OK, so I've looked into this more deeply and I finally remember why we have this comment here. The point is that under_oom shouldn't underflow and that we have to explicitly check for > 0 because a new child memcg could have been added between mem_cgroup_mark_under_oom and mem_cgroup_unmark_under_oom. > >So the comment makes sense although it is not as helpful as it could be. >I think that changing it to the following will be more usefule > > /* > * Be careful about under_oom underflows becase a child memcg > * could have neem added after mem_cgroup_mark_under_oom Should it be s/neem/been/ ? > */ Many thanks for detailed explanation. Will fix it in v2. Thanks again.