linux-kernel - Re: [PATCH 6/8] mm: vmscan: Throttle reclaim if encountering too many dirty pages under writeback

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Message-ID: <20110731151749.GD1735@barrios-desktop>
Date:	Mon, 1 Aug 2011 00:17:49 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	XFS <xfs@....sgi.com>, Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 6/8] mm: vmscan: Throttle reclaim if encountering too
 many dirty pages under writeback

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@...e.de>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

-- 
Kind regards,
Minchan Kim
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