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

[Vivek Goyal <vgoyal@redhat.com>]

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