Re: [PATCH 12/15] swap: do not send discards as barriers

[Chris Mason <chris.mason@oracle.com>]

On Thu, Aug 19, 2010 at 05:02:21AM -0400, Christoph Hellwig wrote:
> On Wed, Aug 18, 2010 at 08:47:52PM -0700, Hugh Dickins wrote:
> > (though if you happened to respin, I'd be be glad for those newlines
> > between GFP_KERNEL, BLKDEV_IFL_WAIT to go away now)
> > 
> > This patch could go in any time now: I may want to push it in and
> > get it to 35-stable, because it certainly helps against the swap
> > discard regression that Nigel reported (though I've not yet seen
> > his numbers with this).  However, I don't think it eliminates the
> > regression, so I've more testing and experimenting to do before
> > deciding about it - the right answer may just be to disable swap
> > discard, as you asked for long ago.
> 
> If we do get a bit testing I'd be almost inclined to drop BLKDEV_IFL_BARRIER
> under the floor for all callers in .36, and also remove BLKDEV_IFL_WAIT,
> as it's now unconditional.  That would allow us to simpliy the
> synchronous interfaces for the two, and give us an easy way to develop
> a proper asynchronous discard interface in the .37 cycle without
> interfering with the barrier rework.  Any comments on that idea from the
> filesystem crowd?
> 

No complaints here.

-chris