On Wednesday 04 February 2009 03:12:45 Chris Mason wrote: > On Tue, 2009-02-03 at 13:11 +1100, Nick Piggin wrote: > > The interesting thing is why is this causing such a slowdown. If there is > > only a single main file active in the workload, then I don't see why this > > patch should make such a big difference. In either case, wouldn't pdflush > > come back and just start writing out from the start of the file anyway? > > Perhaps the difference is that without the patch, pdflush will return > after running congestion_wait()? This would give bdb and iozone a > chance to fill in more pages, and increases the chances we'll do > sequential IO. That's a possible explanation. I'll do some iozone runs and see if I can work out what's going on. If we can distill the "goodness" of the previous offset-wrap behaviour without reverting to make writeout more offset dependent, that would be nice -- it might even benefit other cases that weren't previously hitting the offset wrap case. Worst case, if we can't come up with something simple and obvious for 2.6.29, we can restore the old behaviour until we can come up with something better. Thanks, Nick -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
