linux-kernel - Re: [PATCH memcg v3 1/3] mm, oom: pagefault_out_of_memory: don't force global OOM for dying tasks

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Date:   Mon, 25 Oct 2021 11:27:29 +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>,
        Roman Gushchin <guro@...com>,
        Uladzislau Rezki <urezki@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Shakeel Butt <shakeelb@...gle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        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 1/3] mm, oom: pagefault_out_of_memory: don't
 force global OOM for dying tasks

On Sat 23-10-21 16:19:28, Vasily Averin wrote:
> Any allocation failure during the #PF path will return with VM_FAULT_OOM
> which in turn results in pagefault_out_of_memory which in own turn
> executes out_out_memory() and can kill a random task.
> 
> An allocation might fail when the current task is the oom victim
> and there are no memory reserves left. The OOM killer is already
> handled at the page allocator level for the global OOM and at the
> charging level for the memcg one. Both have much more information
> about the scope of allocation/charge request. This means that
> either the OOM killer has been invoked properly and didn't lead
> to the allocation success or it has been skipped because it couldn't
> have been invoked. In both cases triggering it from here is pointless
> and even harmful.
> 
> It makes much more sense to let the killed task die rather than to
> wake up an eternally hungry oom-killer and send him to choose a fatter
> victim for breakfast.
> 
> Suggested-by: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Vasily Averin <vvs@...tuozzo.com>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
>  mm/oom_kill.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 831340e7ad8b..1deef8c7a71b 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -1137,6 +1137,9 @@ void pagefault_out_of_memory(void)
>  	if (mem_cgroup_oom_synchronize(true))
>  		return;
>  
> +	if (fatal_signal_pending(current))
> +		return;
> +
>  	if (!mutex_trylock(&oom_lock))
>  		return;
>  	out_of_memory(&oc);
> -- 
> 2.32.0

-- 
Michal Hocko
SUSE Labs