linux-kernel - Re: [PATCH v4 1/1] mm: vmscan: Reduce throttling due to a failure to make progress

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Date:   Thu, 2 Dec 2021 08:30:51 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Alexey Avramov <hakavlad@...ox.lv>,
        Rik van Riel <riel@...riel.com>,
        Mike Galbraith <efault@....de>,
        Darrick Wong <djwong@...nel.org>, regressions@...ts.linux.dev,
        Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/1] mm: vmscan: Reduce throttling due to a failure to
 make progress

Hi Mel,

On Thu, Dec 2, 2021 at 7:07 AM Mel Gorman <mgorman@...hsingularity.net> wrote:
>
> Mike Galbraith, Alexey Avramov and Darrick Wong all reported similar
> problems due to reclaim throttling for excessive lengths of time.
> In Alexey's case, a memory hog that should go OOM quickly stalls for
> several minutes before stalling. In Mike and Darrick's cases, a small
> memcg environment stalled excessively even though the system had enough
> memory overall.
>
> Commit 69392a403f49 ("mm/vmscan: throttle reclaim when no progress is being
> made") introduced the problem although commit a19594ca4a8b ("mm/vmscan:
> increase the timeout if page reclaim is not making progress") made it
> worse. Systems at or near an OOM state that cannot be recovered must
> reach OOM quickly and memcg should kill tasks if a memcg is near OOM.
>

Is there a reason we can't simply revert 69392a403f49 instead of adding
more code/heuristics? Looking more into 69392a403f49, I don't think the
code and commit message are in sync.

For the memcg reclaim, instead of just removing congestion_wait or
replacing it with schedule_timeout in mem_cgroup_force_empty(), why
change the behavior of all memcg reclaim. Also this patch effectively
reverts that behavior of 69392a403f49.

For direct reclaimers under global pressure, why is page allocator a bad
place for stalling on no progress reclaim? IMHO the callers of the
reclaim should decide what to do if reclaim is not making progress.

thanks,
Shakeel