linux-kernel - Re: ext3 IO latency measurements

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Message-ID: <49CCBFC4.7070707@cateee.net>
Date:	Fri, 27 Mar 2009 13:00:04 +0100
From:	"Giacomo A. Catenazzi" <cate@...eee.net>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>, Ingo Molnar <mingo@...e.hu>,
	Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	David Rees <drees76@...il.com>, Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Roland McGrath <roland@...hat.com>
Subject: Re: ext3 IO latency measurements

Alan Cox wrote:
>> And what's the argument for not doing it in the kernel?
>>
>> The fact is, "atime" by default is just wrong.
> 
> It probably was a wrong default - twenty years ago. Actually it may well
> have been a wrong default in Unix v6 8)
> 
> However
> - atime behaviour is SuS required

so I propose an other mount option along to strictatime:
nowatime: it give the actual time as atime:
it is totally useless, but fast *and* POSIX compatible:
- no disk writes on accesses
- POSIX doesn't mandate the behaviour of other processes, so
   we simulate that fs are scanned at every fs-tick.
- IMHO more programs break, but in this case only
   the POSIX incompatible programs.


> - there are users with systems out there using atime and dependant on
>   proper atime

This is the real problem.

ciao
	cate

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