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

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Message-ID: <20070805234356.GI31489@sgi.com>
Date:	Mon, 6 Aug 2007 09:43:56 +1000
From:	David Chinner <dgc@....com>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Jakob Oestergaard <jakob@...hought.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	miklos@...redi.hu, akpm@...ux-foundation.org, neilb@...e.de,
	dgc@....com, tomoki.sekiyama.qu@...achi.com,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	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

On Sun, Aug 05, 2007 at 06:42:30AM -0400, Jeff Garzik wrote:
> Jakob Oestergaard wrote:
> >Oh dear.
> >
> >Why not just make ext3 fsync() a no-op while you're at it?
> >
> >Distros can turn it back on if it's needed...
> >
> >Of course I'm not serious, but like atime, fsync() is something one
> 
> No, they are nothing alike, and you are just making yourself look silly 
> if you compare them.  fsync has to do with fundamental guarantees about 
> data.

Hi Jeff - just as a point to note, I think you should check the spec
for fsync before stating that:

"It is explicitly intended that a null implementation is permitted."

and

"... fsync() might or might not actually cause data to be written where it is
safe from a power failure."

http://www.opengroup.org/onlinepubs/009695399/functions/fsync.html

So fsync() does not have to provide the fundamental guarantees you think
it should.

Note - I'm not saying that this is at all sane (it's crazy, IMO), I'm just
pointing out that a "nofsync" mount option to avoid fsync overhead is a
legal thing to do....

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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