linux-kernel - Re: [PATCH 0/9] Reduce latencies and improve overall reclaim efficiency v1

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Date:	Wed, 8 Sep 2010 09:38:51 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/9] Reduce latencies and improve overall reclaim
	efficiency v1

On Wed, Sep 08, 2010 at 12:14:29PM +0900, KOSAKI Motohiro wrote:
> > There have been numerous reports of stalls that pointed at the problem being
> > somewhere in the VM. There are multiple roots to the problems which means
> > dealing with any of the root problems in isolation is tricky to justify on
> > their own and they would still need integration testing. This patch series
> > gathers together three different patch sets which in combination should
> > tackle some of the root causes of latency problems being reported.
> > 
> > The first patch improves vmscan latency by tracking when pages get reclaimed
> > by shrink_inactive_list. For this series, the most important results is
> > being able to calculate the scanning/reclaim ratio as a measure of the
> > amount of work being done by page reclaim.
> > 
> > Patches 2 and 3 account for the time spent in congestion_wait() and avoids
> > calling going to sleep on congestion when it is unnecessary. This is expected
> > to reduce stalls in situations where the system is under memory pressure
> > but not due to congestion.
> > 
> > Patches 4-8 were originally developed by Kosaki Motohiro but reworked for
> > this series. It has been noted that lumpy reclaim is far too aggressive and
> > trashes the system somewhat. As SLUB uses high-order allocations, a large
> > cost incurred by lumpy reclaim will be noticeable. It was also reported
> > during transparent hugepage support testing that lumpy reclaim was trashing
> > the system and these patches should mitigate that problem without disabling
> > lumpy reclaim.
> 
> Wow, I'm sorry my lazyness bother you. I'll join to test this patch series
> ASAP and take a feedback soon.
> 

It did not bother me at all. I generally agreed with the direction and
it seemed sensible to take them into consideration before patches 9 and
10 in particular and make sure they all played nicely together.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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