From: Rik van Riel <riel@redhat.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jiri Slaby <jslaby@suse.cz>,
Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
Zlatko Calusic <zcalusic@bitsync.net>,
Johannes Weiner <hannes@cmpxchg.org>,
dormando <dormando@rydia.net>, Michal Hocko <mhocko@suse.cz>,
Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 7/9] mm: vmscan: Block kswapd if it is encountering pages under writeback
Date: Tue, 14 May 2013 17:06:54 -0400 [thread overview]
Message-ID: <5192A76E.6010509@redhat.com> (raw)
In-Reply-To: <1368432760-21573-8-git-send-email-mgorman@suse.de>
On 05/13/2013 04:12 AM, Mel Gorman wrote:
> Historically, kswapd used to congestion_wait() at higher priorities if it
> was not making forward progress. This made no sense as the failure to make
> progress could be completely independent of IO. It was later replaced by
> wait_iff_congested() and removed entirely by commit 258401a6 (mm: don't
> wait on congested zones in balance_pgdat()) as it was duplicating logic
> in shrink_inactive_list().
>
> This is problematic. If kswapd encounters many pages under writeback and
> it continues to scan until it reaches the high watermark then it will
> quickly skip over the pages under writeback and reclaim clean young
> pages or push applications out to swap.
>
> The use of wait_iff_congested() is not suited to kswapd as it will only
> stall if the underlying BDI is really congested or a direct reclaimer was
> unable to write to the underlying BDI. kswapd bypasses the BDI congestion
> as it sets PF_SWAPWRITE but even if this was taken into account then it
> would cause direct reclaimers to stall on writeback which is not desirable.
>
> This patch sets a ZONE_WRITEBACK flag if direct reclaim or kswapd is
> encountering too many pages under writeback. If this flag is set and
> kswapd encounters a PageReclaim page under writeback then it'll assume
> that the LRU lists are being recycled too quickly before IO can complete
> and block waiting for some IO to complete.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>
> Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Rik van Riel <riel@redhat.com>
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next prev parent reply other threads:[~2013-05-14 21:09 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-13 8:12 [PATCH 0/9] Reduce system disruption due to kswapd V4 Mel Gorman
2013-05-13 8:12 ` [PATCH 1/9] mm: vmscan: Limit the number of pages kswapd reclaims at each priority Mel Gorman
2013-05-13 8:12 ` [PATCH 2/9] mm: vmscan: Obey proportional scanning requirements for kswapd Mel Gorman
2013-05-14 10:21 ` Michal Hocko
2013-05-17 3:41 ` Kamezawa Hiroyuki
2013-05-13 8:12 ` [PATCH 3/9] mm: vmscan: Flatten kswapd priority loop Mel Gorman
2013-05-14 10:38 ` Michal Hocko
2013-05-13 8:12 ` [PATCH 4/9] mm: vmscan: Decide whether to compact the pgdat based on reclaim progress Mel Gorman
2013-05-14 10:51 ` Michal Hocko
2013-05-13 8:12 ` [PATCH 5/9] mm: vmscan: Do not allow kswapd to scan at maximum priority Mel Gorman
2013-05-13 8:12 ` [PATCH 6/9] mm: vmscan: Have kswapd writeback pages based on dirty pages encountered, not priority Mel Gorman
2013-05-14 11:25 ` Michal Hocko
2013-05-13 8:12 ` [PATCH 7/9] mm: vmscan: Block kswapd if it is encountering pages under writeback Mel Gorman
2013-05-14 21:06 ` Rik van Riel [this message]
2013-05-15 21:39 ` Andrew Morton
2013-05-16 13:07 ` Mel Gorman
2013-05-13 8:12 ` [PATCH 8/9] mm: vmscan: Check if kswapd should writepage once per pgdat scan Mel Gorman
2013-05-13 8:12 ` [PATCH 9/9] mm: vmscan: Move logic from balance_pgdat() to kswapd_shrink_zone() Mel Gorman
2013-05-14 12:23 ` Michal Hocko
2013-05-14 21:06 ` Rik van Riel
2013-05-15 20:37 ` [PATCH 0/9] Reduce system disruption due to kswapd V4 Andrew Morton
2013-05-16 10:33 ` Mel Gorman
2013-05-16 13:54 ` Michal Hocko
2013-05-16 14:11 ` Mel Gorman
2013-05-18 21:15 ` Zlatko Calusic
2013-05-21 23:13 ` Dave Chinner
2013-05-22 8:48 ` Mel Gorman
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