linux-kernel - Re: Linux 2.6.29

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Message-ID: <20090327143543.GA17541@infradead.org>
Date:	Fri, 27 Mar 2009 10:35:44 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Theodore Tso <tytso@....edu>, Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jeff Garzik <jeff@...zik.org>, Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>, David Rees <drees76@...il.com>,
	Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29

On Fri, Mar 27, 2009 at 10:13:33AM -0400, Theodore Tso wrote:
> On Fri, Mar 27, 2009 at 08:57:23AM +0100, Jens Axboe wrote:
> > 
> > Here's a simple patch that does that. Not even tested, it compiles. Note
> > that file systems that currently do blkdev_issue_flush() in their
> > ->sync() should then get it removed.
> > 
> 
> That's going to be a mess.  Ext3 implements an fsync() by requesting a
> journal commit, and then waiting for the commit to have taken place.
> The commit happens in another thread, kjournald.  Knowing when it's OK
> not to do a blkdev_issue_flush() because the commit was triggered by
> an fsync() is going to be really messy.  Could we at least have a flag
> in struct super which says, "We'll handle the flush correctly, please
> don't try to do it for us?"

Doing it in vfs_fsync also is completely wrong layering.  If people want
it for simple filesystems add it to file_fsync instead of messing up
the generic helper.  Removing well meaning but ill behaved policy from
the generic path has been costing me far too much time lately.

And please add a tuneable for the flush.  Preferable a generic one at
the block device layer instead of the current mess where every
filesystem has a slightly different option for barrier usage.
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