linux-kernel - Re: [PATCH] mm, vmscan: do not loop on too_many

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Message-ID: <20170309145937.GK11592@dhcp22.suse.cz>
Date:   Thu, 9 Mar 2017 15:59:38 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Rik van Riel <riel@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever

On Thu 09-03-17 09:16:25, Rik van Riel wrote:
> On Thu, 2017-03-09 at 10:12 +0100, Michal Hocko wrote:
> > On Wed 08-03-17 10:54:57, Rik van Riel wrote:
> 
> > > In fact, false OOM kills with that kind of workload is
> > > how we ended up getting the "too many isolated" logic
> > > in the first place.
> > Right, but the retry logic was considerably different than what we
> > have these days. should_reclaim_retry considers amount of reclaimable
> > memory. As I've said earlier if we see a report where the oom hits
> > prematurely with many NR_ISOLATED* we know how to fix that.
> 
> Would it be enough to simply reset no_progress_loops
> in this check inside should_reclaim_retry, if we know
> pageout IO is pending?
> 
>                         if (!did_some_progress) {
>                                 unsigned long write_pending;
> 
>                                 write_pending = zone_page_state_snapshot(zone,
>                                                         NR_ZONE_WRITE_PENDING);
> 
>                                 if (2 * write_pending > reclaimable) {
>                                         congestion_wait(BLK_RW_ASYNC, HZ/10);
>                                         return true;
>                                 }
>                         }

I am not really sure what problem we are trying to solve right now to be
honest. I would prefer to keep the logic simpler rather than over
engeneer something that is even not needed.

-- 
Michal Hocko
SUSE Labs