linux-kernel - Re: [PATCH 5/5] mm: writeback: Prioritise dirty inodes encountered by direct reclaim for background flushing

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Message-ID: <20110714154915.GV7529@suse.de>
Date:	Thu, 14 Jul 2011 16:49:15 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	XFS <xfs@....sgi.com>, Dave Chinner <david@...morbit.com>,
	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: [PATCH 5/5] mm: writeback: Prioritise dirty inodes encountered
 by direct reclaim for background flushing

On Thu, Jul 14, 2011 at 11:09:59AM -0400, Christoph Hellwig wrote:
> On Wed, Jul 13, 2011 at 03:31:27PM +0100, Mel Gorman wrote:
> > It is preferable that no dirty pages are dispatched from the page
> > reclaim path. If reclaim is encountering dirty pages, it implies that
> > either reclaim is getting ahead of writeback or use-once logic has
> > prioritise pages for reclaiming that are young relative to when the
> > inode was dirtied.
> 
> what does this buy us? 

Very little. The vague intention was to avoid a situation where kswapds
priority was raised such that it had to write pages to clean a
particular zone.

> If at all we should prioritize by a zone,
> e.g. tell write_cache_pages only to bother with writing things out
> if the dirty page is in a given zone.   We'd probably still cluster
> around it to make sure we get good I/O patterns, but would only start
> I/O if it has a page we actually care about.
> 

That would make more sense. I've dropped this patch entirely.

-- 
Mel Gorman
SUSE Labs
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