Re: notes on volatile write caches vs fdatasync

[Jeff Garzik]

On 08/27/2009 02:49 PM, Christoph Hellwig wrote:
> On Thu, Aug 27, 2009 at 03:02:52PM +0200, Jan Kara wrote:
> >    I've noticed this as well when we were tracking some problems Pavel
> > Machek found with his USB stick. I even wrote a patch at the time
> >    http://osdir.com/ml/linux-ext4/2009-01/msg00015.html
> > but it somehow died out. Now, the situation should be simpler with
> > fsync paths cleaned up... BTW: People wanted this to be configurable per
> > block device which probably makes sence...
>
> Yeah, that patch is pretty ugly.  We need to do these cache flushes
> in ->fsync (and ->sync_fs if any filesystem really doesn't guarantee to
> issue  transaction there after data has been written).  Adding it
> to simple_fsync too sounds good to me.

Agreed.  That was the direction I was heading with my patch[1].  Last 
feedback I got on that was needing to add a knob to optionally disable 
this new cache-flush behavior.

	Jeff



[1] http://lkml.org/lkml/2009/3/27/366
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