On Thu, Jun 09, 2011 at 08:11:17PM +0800, Wu Fengguang wrote: > > This waits for the I/O completion to actually arrive - something that > > XFS does correctly in both sync and fsync, but ext4 only does for fsync. > > Will it benefit to flush the disk _once_ at the end of sync? > (perhaps it's not be as easy in complex storage setups or whatever) XFS currently does it's own passes over data and metadata in sync. To some extent they are overkill, but things like the iowait that's prominent in your trace actually is needed to catch all in-flight direct I/O. > It's definitely a problem that cfq delays async writes too much. > However in Carlos's report, > > https://bugzilla.kernel.org/attachment.cgi?id=61222 > > there are no sync(1) or fsync running at all. So it may be indicating > a different problem. If you have a heavy read load we still need to write back timestamps, and it kinda sounds like he's hitting that. No guarantee that actuall is the cause, though. -- 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
