Hello, Christoph. On 08/13/2010 01:48 PM, Christoph Hellwig wrote: > The patchset looks functionally correct to me, and with a small patch > to make use of WRITE_FUA_FLUSH survives xfstests, and instrumenting the > underlying qemu shows that we actually get the flush requests where we should. Great. > No performance or power fail testing done yet. > > But I do not like the transition very much. The new WRITE_FUA_FLUSH > request is exactly what filesystems expect from a current barrier > request, so I'd rather move to that functionality without breaking stuff > inbetween. > > So if it was to me I'd keep patches 1, 2, 4 and 5 from your series, than > a main one to relax barrier semantics, then have the renaming patches 7 > and 8, and possible keep patch 11 separate from the main implementation > change, and if absolutely also a separate one to introduce REQ_FUA and > REQ_FLUSH in the bio interface, but keep things working while doing > this. There are two reason to avoid changing the meaning of REQ_HARDBARRIER and just deprecate it. One is to avoid breaking filesystems' expectations underneath it. Please note that there are out-of-tree filesystems too. I think it would be too dangerous to relax REQ_HARDBARRIER. Another is that pseudo block layer drivers (loop, virtio_blk, md/dm...) have assumptions about REQ_HARDBARRIER behavior and things would be broken in obscure ways between REQ_HARDBARRIER semantics change and updates to each of those drivers, so I don't really think changing the semantics while the mechanism is online is a good idea. > Then we can patches do disable the reiserfs barrier "optimization" as > the very first one, and DM/MD support which I'm currently working on > as the last one and we can start doing the heavy testing. Oops, I've already converted loop, virtio_blk/lguest and am working on md/dm right now too. I'm almost done with md and now doing dm. :-) Maybe we should post them right now so that we don't waste too much time trying to solve the same problems? Thanks. -- tejun -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
