[PATCH] xfs: improve metadata I/O merging in the elevator

[Christoph Hellwig]

On Mon, Nov 16, 2009 at 02:50:19PM +1100, Dave Chinner wrote:
> Definitely should be done, but....
> 
> It looks like the patch you posted isn't quite doing what was
> intended - async write buffers are being classified as WRITE, not
> WRITE_META. That means we get more write combining in the elevator
> (performance increase) like with WRITE_META, but don't get the
> faster dispatch (latency reduction) by using the META queue to keep
> the metadata writeback separate from the bulk data writeback.
> That may be why deadline is not showing any improvement...
> 
> FWIW, the original patch here:
> 
> http://oss.sgi.com/archives/xfs/2008-01/msg00630.html
> 
> uses WRITE_META, but it looks like you've taken bits of this
> patch:

Indeed.  I'l re-add the write-side markings and will re-bench and
re-submit.