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

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Date:	05 Aug 2007 02:26:53 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, miklos@...redi.hu,
	akpm@...ux-foundation.org, 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
Subject: Re: [PATCH 00/23] per device dirty throttling -v8

Ingo Molnar <mingo@...e.hu> writes:
> 
> yeah, it's really ugly. But otherwise i've got no real complaint about 
> ext3 - with the obligatory qualification that "noatime,nodiratime" in 
> /etc/fstab is a must. This speeds up things very visibly - especially 
> when lots of files are accessed. It's kind of weird that every Linux 
> desktop and server is hurt by a noticeable IO performance slowdown due 
> to the constant atime updates, while there's just two real users of it: 
> tmpwatch [which can be configured to use ctime so it's not a big issue] 
> and some backup tools. (Ok, and mail-notify too i guess.) Out of tens of 
> thousands of applications. So for most file workloads we give Windows a 
> 20%-30% performance edge, for almost nothing. (for RAM-starved kernel 
> builds the performance difference between atime and noatime+nodiratime 
> setups is more on the order of 40%)

I always thought the right solution would be to just sync atime only
very very lazily. This means if a inode is only dirty because of an
atime update put it on a "only write out when there is nothing to do
or the memory is really needed" list.

-Andi
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