linux-kernel - Re: [PATCH 6/6] vmscan: Kick flusher threads to clean pages when reclaim is encountering dirty pages

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Message-ID: <20100802183109.GJ3278@quack.suse.cz>
Date:	Mon, 2 Aug 2010 20:31:10 +0200
From:	Jan Kara <jack@...e.cz>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Hellwig <hch@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 6/6] vmscan: Kick flusher threads to clean pages when
 reclaim is encountering dirty pages

On Sat 31-07-10 11:33:22, Mel Gorman wrote:
> On Fri, Jul 30, 2010 at 03:06:01PM -0700, Andrew Morton wrote:
> > Sigh.  We have sooo many problems with writeback and latency.  Read
> > https://bugzilla.kernel.org/show_bug.cgi?id=12309 and weep.
> 
> You aren't joking.
> 
> > Everyone's
> > running away from the issue and here we are adding code to solve some
> > alleged stack-overflow problem which seems to be largely a non-problem,
> > by making changes which may worsen our real problems.
> > 
> 
> As it is, filesystems are beginnning to ignore writeback from direct
> reclaim - such as xfs and btrfs. I'm lead to believe that ext3
> effectively ignores writeback from direct reclaim although I don't have
> access to code at the moment to double check (am on the road). So either
> way, we are going to be facing this problem so the VM might as well be
> aware of it :/
  Umm, ext3 should be handling direct reclaim just fine. ext4 does however
ignore it when a page does not have block already allocated (which is a
common case with delayed allocation).

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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