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

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Date:	Sun, 05 Aug 2007 13:59:24 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Theodore Tso <tytso@....edu>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Claudio Martins <ctpm@....utl.pt>,
	Jörn Engel <joern@...fs.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, 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, david@...g.hm
Subject: Re: [PATCH 00/23] per device dirty throttling -v8

Ingo Molnar wrote:
> * Theodore Tso <tytso@....edu> wrote:
> 
>> If you are always reading from the same small set of files (i.e., a 
>> database workload), then those inodes only get updated every 5 seconds 
>> (the traditional/default metadata update sync time, as well as the 
>> default ext3 journal update time), it's no big deal.  Or if you are 
>> running a mail server, most of the time the mail queue files are 
>> getting updated anyway as you process them, and usually the mail is 
>> delivered before 5 seconds is up anyway.
>>
>> So earlier, when Ingo characterized it as, "whenever you read from a 
>> file, even one in memory cache.... do a write!", it's probably a bit 
>> unfair.  Traditional Unix systems simply had very different workload 
>> characteristics than many modern dekstop systems today.
> 
> yeah, i didnt mean to say that it is _always_ a big issue, but "only a 
> small number of files are read" is a very, very small minority of even 
> the database server world.

OTOH, consider a popular Linux task, web serving.  atime results in a 
lot of unnecessary disk traffic.

	Jeff



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