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. > If this becomes widely used, would it be better to snapshot on > wait_for_stable_page instead of on io submission? That really depends on how long you can afford to wait and how much free memory you have. :) It's all a big tradeoff between write latency and consumption of memory pages and bandwidth, and one that I doubt I'm qualified to make for everyone. > FWIW, I'm about to pound pretty hard on this whole patchset on a box > that doesn't need stable pages. I'll let you know how it goes. Yay! --D -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
