On 01/19/2012 01:22 AM, Jan Kara wrote: > On Wed 18-01-12 14:58:08, Darrick J. Wong wrote: >> On Tue, Jan 17, 2012 at 10:36:48PM +0100, Jan Kara wrote: >>> On Tue 17-01-12 15:06:12, Mike Snitzer wrote: >>>> 5) Any more progress on stable pages? >>>> - I know Darrick Wong had some proposals, what remains? >>> As far as I know this is done for XFS, btrfs, ext4. Is more needed? >> >> Yep, it's done for those three fses. >> >> I suppose it might help some people if instead of wait_on_page_writeback we >> could simply page-migrate all the processes onto a new page...? > Well, but it will cost some more memory & copying so whether it's faster > or not pretty much depends on the workload, doesn't it? Anyway I've already > heard one guy complaining that his RT application does redirtying of mmaped > pages and it started seeing big latencies due to stable pages work. So for > these guys migrating might be an option (or maybe fadvise/madvise flag to > do copy out before submitting for IO?). > OK That one is interesting. Because I'd imagine that the Kernel would not start write-out on a busily modified page. Some heavy modifying then a single write. If it's not so then there is already great inefficiency, just now exposed, but was always there. The "page-migrate" mentioned here will not help. Could we not better our page write-out algorithms to avoid heavy contended pages? Do you have a more detailed description of the workload? Is it theoretically avoidable? >> Or possibly modify md-raid5 not to snapshot dirty pages prior to xor/write? >> (I never really bothered to find out if it really does this.) md-raid5/1 currently copies all pages if that what you meant. > Not sure either. Neil should know :) (added to CC). > > Honze Thanks Boaz -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
