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From: Michal Hocko <mhocko@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	Rik van Riel <riel@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever
Date: Mon, 24 Jul 2017 08:50:49 +0200
Message-ID: <20170724065048.GB25221@dhcp22.suse.cz> (raw)
In-Reply-To: <20170721160104.9f6101b9e8de53638b3b853a@linux-foundation.org>

On Fri 21-07-17 16:01:04, Andrew Morton wrote:
> On Thu, 20 Jul 2017 08:56:26 +0200 Michal Hocko <mhocko@kernel.org> wrote:
> > 
> > > > --- a/mm/vmscan.c
> > > > +++ b/mm/vmscan.c
> > > > @@ -1713,9 +1713,15 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
> > > >  	int file = is_file_lru(lru);
> > > >  	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> > > >  	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
> > > > +	bool stalled = false;
> > > >  
> > > >  	while (unlikely(too_many_isolated(pgdat, file, sc))) {
> > > > -		congestion_wait(BLK_RW_ASYNC, HZ/10);
> > > > +		if (stalled)
> > > > +			return 0;
> > > > +
> > > > +		/* wait a bit for the reclaimer. */
> > > > +		schedule_timeout_interruptible(HZ/10);
> > > 
> > > a) if this task has signal_pending(), this falls straight through
> > >    and I suspect the code breaks?
> > 
> > It will not break. It will return to the allocation path more quickly
> > but no over-reclaim will happen and it will/should get throttled there.
> > So nothing critical.
> > 
> > > b) replacing congestion_wait() with schedule_timeout_interruptible()
> > >    means this task no longer contributes to load average here and it's
> > >    a (slightly) user-visible change.
> > 
> > you are right. I am not sure it matters but it might be visible.
> >  
> > > c) msleep_interruptible() is nicer
> > > 
> > > d) IOW, methinks we should be using msleep() here?
> > 
> > OK, I do not have objections. Are you going to squash this in or want a
> > separate patch explaining all the above?
> 
> I'd prefer to have a comment explaining why interruptible sleep is
> being used, because that "what if signal_pending()" case is rather a
> red flag.

I didn't really consider interruptible vs. uninterruptible sleep so it
wasn't really a deliberate decision. Now, that you have brought up the
above points I am OK changing that the uninterruptible.

Here is a fix up. I am fine with this either folded in or as a separate
patch.
---

  reply index

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-10  7:48 Michal Hocko
2017-07-10 13:16 ` Vlastimil Babka
2017-07-10 13:58 ` Rik van Riel
2017-07-10 16:58   ` Johannes Weiner
2017-07-10 17:09     ` Michal Hocko
2017-07-19 22:20 ` Andrew Morton
2017-07-20  6:56   ` Michal Hocko
2017-07-21 23:01     ` Andrew Morton
2017-07-24  6:50       ` Michal Hocko [this message]
2017-07-20  1:54 ` Hugh Dickins
2017-07-20 10:44   ` Tetsuo Handa
2017-07-24  7:01     ` Hugh Dickins
2017-07-24 11:12       ` Tetsuo Handa
2017-07-20 13:22   ` Michal Hocko
2017-07-24  7:03     ` Hugh Dickins
  -- strict thread matches above, loose matches on Subject: below --
2017-03-07 13:30 Michal Hocko
2017-03-07 19:52 ` Rik van Riel
2017-03-08  9:21   ` Michal Hocko
2017-03-08 15:54     ` Rik van Riel
2017-03-09  9:12       ` Michal Hocko
2017-03-09 14:16         ` Rik van Riel
2017-03-09 14:59           ` Michal Hocko
2017-03-09 18:05   ` Johannes Weiner
2017-03-09 22:18     ` Rik van Riel
2017-03-10 10:27       ` Michal Hocko
2017-03-10 10:20     ` Michal Hocko
2017-03-10 11:44       ` Tetsuo Handa
2017-03-21 10:37         ` Tetsuo Handa
2017-04-23 10:24         ` Tetsuo Handa
2017-04-24 12:39           ` Stanislaw Gruszka
2017-04-24 13:06             ` Tetsuo Handa
2017-04-25  6:33               ` Stanislaw Gruszka
2017-06-30  0:14         ` Tetsuo Handa
2017-06-30 13:32           ` Michal Hocko
2017-06-30 15:59             ` Tetsuo Handa
2017-06-30 16:19               ` Michal Hocko
2017-07-01 11:43                 ` Tetsuo Handa
2017-07-05  8:19                   ` Michal Hocko
2017-07-05  8:20                   ` Michal Hocko
2017-07-06 10:48                     ` Tetsuo Handa
2017-03-09 14:31 ` Mel Gorman

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