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

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Message-ID: <46BBAF82.7020702@tmr.com>
Date:	Thu, 09 Aug 2007 20:21:22 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"Martin J. Bligh" <mbligh@...igh.org>,
	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.
> 
I would think that (really) updating atime on open would be enough, 
hopefully without being too much. The "lazyatime" thing I was playing 
with only updated on open, final close, write, and fork.

I like the idea of updating once in a while, but one of the benefits of 
noatime is allowing drives to spin down via inactivity. If something 
does get done in the area of less but non-zero atime tracking, perhaps 
that could be taken into account. I have to check what "laptop_mode 
actually does, since my laptops are old installs.

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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