From: Andrew Morton <akpm@linux-foundation.org>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mel Gorman <mel@csn.ul.ie>, Johannes Weiner <hannes@cmpxchg.org>,
Rik van Riel <riel@redhat.com>, Michal Hocko <mhocko@suse.cz>,
Kent Overstreet <kent.overstreet@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [patch] vmscan: fix zone shrinking exit when scan work is done
Date: Wed, 9 Feb 2011 12:05:50 -0800 [thread overview]
Message-ID: <20110209120550.2bd18590.akpm@linux-foundation.org> (raw)
In-Reply-To: <20110209182846.GN3347@random.random>
On Wed, 9 Feb 2011 19:28:46 +0100
Andrea Arcangeli <aarcange@redhat.com> wrote:
> On Wed, Feb 09, 2011 at 04:46:56PM +0000, Mel Gorman wrote:
> > On Wed, Feb 09, 2011 at 04:46:06PM +0100, Johannes Weiner wrote:
> > > Hi,
> > >
> > > I think this should fix the problem of processes getting stuck in
> > > reclaim that has been reported several times.
> >
> > I don't think it's the only source but I'm basing this on seeing
> > constant looping in balance_pgdat() and calling congestion_wait() a few
> > weeks ago that I haven't rechecked since. However, this looks like a
> > real fix for a real problem.
>
> Agreed. Just yesterday I spent some time on the lumpy compaction
> changes after wondering about Michal's khugepaged 100% report, and I
> expected some fix was needed in this area (as I couldn't find any bug
> in khugepaged yet, so the lumpy compaction looked the next candidate
> for bugs).
>
> I've also been wondering about the !nr_scanned check in
> should_continue_reclaim too but I didn't look too much into the caller
> (I was tempted to remove it all together). I don't see how checking
> nr_scanned can be safe even after we fix the caller to avoid passing
> non-zero values if "goto restart".
>
> nr_scanned is incremented even for !page_evictable... so it's not
> really useful to insist, just because we scanned something, in my
> view. It looks bogus... So my proposal would be below.
>
> ====
> Subject: mm: stop checking nr_scanned in should_continue_reclaim
>
> From: Andrea Arcangeli <aarcange@redhat.com>
>
> nr_scanned is incremented even for !page_evictable... so it's not
> really useful to insist, just because we scanned something.
So if reclaim has scanned 100% !page_evictable pages,
should_continue_reclaim() can return true and we keep on scanning?
That sounds like it's both good and bad :( Is this actually a problem?
What sort of behaviour could it cause and under what circumstances?
Johannes's patch is an obvious bugfix and I'll run with it for now, but
please let's have a further think abut the impact of the
!page_evictable pages.
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next prev parent reply other threads:[~2011-02-09 20:06 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-09 15:46 [patch] vmscan: fix zone shrinking exit when scan work is done Johannes Weiner
2011-02-09 15:54 ` Kent Overstreet
2011-02-09 16:46 ` Mel Gorman
2011-02-09 18:28 ` Andrea Arcangeli
2011-02-09 20:05 ` Andrew Morton [this message]
2011-02-10 10:21 ` Mel Gorman
2011-02-10 10:41 ` Michal Hocko
2011-02-10 12:48 ` Andrea Arcangeli
2011-02-10 13:33 ` Mel Gorman
2011-02-10 14:14 ` Andrea Arcangeli
2011-02-10 14:58 ` Mel Gorman
2011-02-16 9:50 ` [PATCH] mm: vmscan: Stop reclaim/compaction earlier due to insufficient progress if !__GFP_REPEAT Mel Gorman
2011-02-16 10:13 ` Andrea Arcangeli
2011-02-16 11:22 ` Mel Gorman
2011-02-16 14:44 ` Andrea Arcangeli
2011-02-16 12:03 ` Andrea Arcangeli
2011-02-16 12:14 ` Rik van Riel
2011-02-16 12:38 ` Johannes Weiner
2011-02-16 23:26 ` Minchan Kim
2011-02-17 22:22 ` Andrew Morton
2011-02-18 12:22 ` Mel Gorman
2011-02-10 4:04 ` [patch] vmscan: fix zone shrinking exit when scan work is done Minchan Kim
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