linux-kernel - Re: [PATCH memcg v3] memcg: prohibit unconditional exceeding the limit of dying tasks

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Date:   Tue, 5 Oct 2021 16:55:13 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel@...nvz.org
Subject: Re: [PATCH memcg v3] memcg: prohibit unconditional exceeding the
 limit of dying tasks

On Tue 05-10-21 16:52:31, Vasily Averin wrote:
> v3: no functional changes, just improved patch description

You haven't addressed my review feedback regarding the oom invocation.
Let me paste it here again:
: > @@ -1607,7 +1607,7 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
: >        * A few threads which were not waiting at mutex_lock_killable() can
: >        * fail to bail out. Therefore, check again after holding oom_lock.
: >        */
: > -     ret = should_force_charge() || out_of_memory(&oc);
: > +     ret = task_is_dying() || out_of_memory(&oc);
: 
: task_is_dying check will prevent the oom killer for dying tasks. There
: is an additional bail out at out_of_memory layer. These checks are now
: leading to a completely different behavior. Currently we simply use
: "unlimited" reserves and therefore we do not have to kill any task. Now
: the charge fails without using all reclaim measures. So I believe we
: should drop those checks for memcg oom paths. I have to think about this
: some more because I might be missing some other side effects.
-- 
Michal Hocko
SUSE Labs