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Re: [PATCH 6/8] mm: vmscan: Throttle reclaim if encountering too many di

To: Mel Gorman <mgorman@xxxxxxx>
Subject: Re: [PATCH 6/8] mm: vmscan: Throttle reclaim if encountering too many dirty pages under writeback
From: Minchan Kim <minchan.kim@xxxxxxxxx>
Date: Mon, 1 Aug 2011 00:17:49 +0900
Cc: Linux-MM <linux-mm@xxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, XFS <xfs@xxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Johannes Weiner <jweiner@xxxxxxxxxx>, Wu Fengguang <fengguang.wu@xxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>
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References: <1311265730-5324-1-git-send-email-mgorman@xxxxxxx> <1311265730-5324-7-git-send-email-mgorman@xxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Jul 21, 2011 at 05:28:48PM +0100, Mel Gorman wrote:
> Workloads that are allocating frequently and writing files place a
> large number of dirty pages on the LRU. With use-once logic, it is
> possible for them to reach the end of the LRU quickly requiring the
> reclaimer to scan more to find clean pages. Ordinarily, processes that
> are dirtying memory will get throttled by dirty balancing but this
> is a global heuristic and does not take into account that LRUs are
> maintained on a per-zone basis. This can lead to a situation whereby
> reclaim is scanning heavily, skipping over a large number of pages
> under writeback and recycling them around the LRU consuming CPU.
> 
> This patch checks how many of the number of pages isolated from the
> LRU were dirty. If a percentage of them are dirty, the process will be
> throttled if a blocking device is congested or the zone being scanned
> is marked congested. The percentage that must be dirty depends on
> the priority. At default priority, all of them must be dirty. At
> DEF_PRIORITY-1, 50% of them must be dirty, DEF_PRIORITY-2, 25%
> etc. i.e.  as pressure increases the greater the likelihood the process
> will get throttled to allow the flusher threads to make some progress.
> 
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>

-- 
Kind regards,
Minchan Kim

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