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

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Message-ID: <20110603013345.GD27129@redhat.com>
Date:	Thu, 2 Jun 2011 21:33:45 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	"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 09:28:58PM -0400, Vivek Goyal wrote:
> On Thu, Jun 02, 2011 at 09:02:33PM -0400, 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.  XFS is beeing rather stupid about the
> > amount of synchronization it requires.  The untested patch below
> > should help with avoiding the synchronization if you're purely doing
> > overwrites:
> 
> Yes this patch helps. I have already laid out the file and doing
> overwrites.
> 
> I throttled aio-stress in one cgroup to 1 byte/sec and edited another
> file from other cgroup and did a "sync" and it completed.

Even other test where I am running aio-stress in one window and edited
a file in another window and typed "sync" worked. "sync" does not hang
waiting for aio-stress to finish.

Thanks
Vivek
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