From: Mel Gorman <mel@csn.ul.ie>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
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 16:46:56 +0000 [thread overview]
Message-ID: <20110209164656.GA1063@csn.ul.ie> (raw)
In-Reply-To: <20110209154606.GJ27110@cmpxchg.org>
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.
> Kent actually
> single-stepped through this code and noted that it was never exiting
> shrink_zone(), which really narrowed it down a lot, considering the
> tons of nested loops from the allocator down to the list shrinking.
>
> Hannes
>
> ---
> From: Johannes Weiner <hannes@cmpxchg.org>
> Subject: vmscan: fix zone shrinking exit when scan work is done
>
> '3e7d344 mm: vmscan: reclaim order-0 and use compaction instead of
> lumpy reclaim' introduced an indefinite loop in shrink_zone().
>
> It meant to break out of this loop when no pages had been reclaimed
> and not a single page was even scanned. The way it would detect the
> latter is by taking a snapshot of sc->nr_scanned at the beginning of
> the function and comparing it against the new sc->nr_scanned after the
> scan loop. But it would re-iterate without updating that snapshot,
> looping forever if sc->nr_scanned changed at least once since
> shrink_zone() was invoked.
>
> This is not the sole condition that would exit that loop, but it
> requires other processes to change the zone state, as the reclaimer
> that is stuck obviously can not anymore.
>
> This is only happening for higher-order allocations, where reclaim is
> run back to back with compaction.
>
> Reported-by: Michal Hocko <mhocko@suse.cz>
> Reported-by: Kent Overstreet <kent.overstreet@gmail.com>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Well spotted.
Acked-by: Mel Gorman <mel@csn.ul.ie>
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2011-02-09 16:47 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 [this message]
2011-02-09 18:28 ` Andrea Arcangeli
2011-02-09 20:05 ` Andrew Morton
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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