On Thu, Sep 03, 2009 at 03:52:01PM +1000, Dave Chinner wrote:

quoted

XFS did the mistake of trusting the VM, while everyone more or less
overrode it.  Removing all those checks and writing out much larger
data fixes it with a relatively small patch:

	http://verein.lst.de/~hch/xfs/xfs-writeback-scaling

Careful:

-	tloff = min(tlast, startpage->index + 64);
+	tloff = min(tlast, startpage->index + 8192);

That will cause 64k page machines to try to write back 512MB at a
time. This will re-introduce similar to the behaviour in sles9 where
writeback would only terminate at the end of an extent (because the
mapping end wasn't capped like above).

Pretty good point, any applies to all the different things we discussed
recently.  Ted, should be maybe introduce a max_writeback_mb instead of
the max_writeback_pages in the VM, too?