On Fri, Dec 14, 2012 at 02:33:34PM +1100, Dave Chinner wrote: > On Thu, Dec 13, 2012 at 06:10:49PM -0800, Darrick J. Wong wrote: > > On Thu, Dec 13, 2012 at 05:48:06PM -0800, Andy Lutomirski wrote: > > > On 12/13/2012 12:08 AM, Darrick J. Wong wrote: > > > > Several complaints have been received regarding long file write > > > > latencies when > > > > memory pages must be held stable during writeback. Since it might not > > > > be > > > > acceptable to stall programs for the entire duration of a page write > > > > (which may > > > > take many milliseconds even on good hardware), enable a second strategy > > > > wherein > > > > pages are snapshotted as part of submit_bio; the snapshot can be held > > > > stable > > > > while writes continue. > > > > > > > > This provides a band-aid to provide stable page writes on jbd without > > > > needing > > > > to backport the fixed locking scheme in jbd2. A mount option is added > > > > to ext4 > > > > to allow administrators to enable it there. > > > > > > I'm a bit confused as to what it has to do with ext3. Wouldn't this be > > > useful as a mount option everywhere, though? > > > > ext3 requires snapshots; the rest are ok with either strategy. > > > > *If* snapshotting is generally liked, then yes I'll go redo it as a vfs > > mount > > option. > > It's copying every single IO, right? If so, then please don't > propagate any further than is necessary to fix the broken > filesystems...
Yup. I wasn't intending this flag for general service, though I /am/ curious to hear if anyone sees any substantive performance difference with snapshots. --D > > Cheers, > > Dave. > -- > Dave Chinner > da...@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
