linux-kernel - Re: [RFC PATCH 0/8] Reduce filesystem writeback from page reclaim v2

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Message-ID: <20110726112055.GC8048@dastard>
Date:	Tue, 26 Jul 2011 21:20:55 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	XFS <xfs@....sgi.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>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [RFC PATCH 0/8] Reduce filesystem writeback from page reclaim v2

On Thu, Jul 21, 2011 at 05:28:42PM +0100, Mel Gorman wrote:
> Warning: Long post with lots of figures. If you normally drink coffee
> and you don't have a cup, get one or you may end up with a case of
> keyboard face.

[snip]

> Overall, having kswapd avoiding writes does improve performance
> which is not a surprise. Dave asked "do we even need IO at all from
> reclaim?". On NUMA machines, the answer is "yes" unless the VM can
> wake the flusher thread to clean a specific node.

Great answer, Mel. ;)

> When kswapd never
> writes, processes can stall for significant periods of time waiting on
> flushers to clean the correct pages. If all writing is to be deferred
> to flushers, it must ensure that many writes on one node would not
> starve requests for cleaning pages on another node.

Ok, so that's a direction we need to work towards, then.

> I'm currently of the opinion that we should consider merging patches
> 1-7 and discuss what is required before merging. It can be tackled
> later how the flushers can prioritise writing of pages belonging to
> a particular zone before disabling all writes from reclaim.

Sounds reasonable to me.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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