On Fri, Dec 14, 2012 at 05:12:37PM -0800, Andy Lutomirski wrote: > On Thu, Dec 13, 2012 at 6:10 PM, Darrick J. Wong > <darrick.wong@xxxxxxxxxx> 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. > > > >> 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 > > It survived. I hit at least one mm bug, but I really don't think it's > a problem with your code. (I have not tried this workload on Linux > 3.7 at all before. It normally runs on 3.5.) The box in question is Would you mind sending along the bug report so I can make sure? > ext4 on LVM on dm-crypt on (hardware) RAID 5 on hpsa, which should not > need stable pages. > > The majority of the data written (that wasn't unlinked before it was > dropped from cache) was checksummed when written and verified later. > Most of this data was written using mmap. This workload hammers the > vm concurrently in several threads, and it frequently stalls when > stable pages are enabled, so it's probably exercising the code > decently well. Did you observe any change in performance? > Feel free to add Tested-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Will do! Thanks for the testing! --D -- 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
