linux-ext4 - Re: Query about DIO/AIO WRITE throttling and ext4 serialization

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Message-ID: <20110603050055.GA6136@infradead.org>
Date:	Fri, 3 Jun 2011 01:00:55 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Vivek Goyal <vgoyal@...hat.com>, Ted Ts'o <tytso@....edu>,
	Dave Chinner <david@...morbit.com>, linux-ext4@...r.kernel.org
Subject: Re: Query about DIO/AIO WRITE throttling and ext4 serialization

On Thu, Jun 02, 2011 at 10:30:38PM -0500, Eric Sandeen wrote:
> On 6/2/11 8:02 PM, Christoph Hellwig wrote:
> > On Thu, Jun 02, 2011 at 08:54:03PM -0400, Vivek Goyal wrote:
> >> Just wondering why ext4 and XFS behavior are different and which is a
> >> more appropriate behavior. ext4 does not seem to be waiting for all
> >> pending AIO/DIO to finish while XFS does.
> > 
> > They're both wrong.  Ext4 completely misses support in fsync or sync
> > to catch pending unwrittent extent conversions, and thus fails to obey
> > the data integrity guarante.  
> 
> I'm not sure about that.
> 
> ext4_sync_file() does ext4_flush_completed_IO() which does:

> Granted, I get easily lost in ext4's codepaths here, which is actually
> why I suggested Vivek pose these questions to the list ;)

You're right it gets fsync right, but the sync still seems to be missing,
which does not just include sync, but also the syncfs system call
and unmount.

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