linux-kernel - Re: [PATCH 00/23] per device dirty throttling -v8

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Message-ID: <46BA65E1.8010704@mbligh.org>
Date:	Wed, 08 Aug 2007 17:54:57 -0700
From:	Martin Bligh <mbligh@...igh.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	J??rn Engel <joern@...fs.org>, Ingo Molnar <mingo@...e.hu>,
	Jeff Garzik <jeff@...zik.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	miklos@...redi.hu, neilb@...e.de, dgc@....com,
	tomoki.sekiyama.qu@...achi.com, nikita@...sterfs.com,
	trond.myklebust@....uio.no, yingchao.zhou@...il.com,
	richard@....demon.co.uk, david@...g.hm
Subject: Re: [PATCH 00/23] per device dirty throttling -v8

Andrew Morton wrote:
> On Wed, 08 Aug 2007 14:10:15 -0700
> "Martin J. Bligh" <mbligh@...igh.org> wrote:
> 
>> Why isn't this easily fixable by just adding an additional dirty
>> flag that says atime has changed? Then we only cause a write
>> when we remove the inode from the inode cache, if only atime
>> is updated.
> 
> I think that could be made to work, and it would fix the performance
> issue.
> 
> It is a behaviour change.  At present ext3 (for example) commits everything
> every five seconds.  After a change like this, a crash+recovery could cause
> a file's atime to go backwards by an arbitrarily large time interval - it
> could easily be months.

A second pdflush / workqueue at a slower rate would alleviate that.

Yes, it's a semantic change ... but only in an incredibly small
corner-case ?

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