On Mon, 29 Oct 2012 19:30:51 +0100 Jan Kara <jack@xxxxxxx> wrote: > On Mon 29-10-12 19:13:58, Jan Kara wrote: > > On Fri 26-10-12 18:35:24, Darrick J. Wong wrote: > > > This creates BDI_CAP_STABLE_WRITES, which indicates that a device requires > > > stable page writes. It also plumbs in a sysfs attribute so that admins can > > > check the device status. > > > > > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > I guess Jens Axboe <axboe@xxxxxxxxx> would be the best target for this > > patch (so that he can merge it). The patch looks OK to me. You can add: > > Reviewed-by: Jan Kara <jack@xxxxxxx> > One more thing popped up in my mind: What about NFS, Ceph or md RAID5? > These could (at least theoretically) care about stable writes as well. I'm > not sure if they really started to use them but it would be good to at > least let them know. > What exactly are the semantics of BDI_CAP_STABLE_WRITES ? If I set it for md/RAID5, do I get a cast-iron guarantee that no byte in any page submitted for write will ever change until after I call bio_endio()? If so, is this true for all filesystems? - I would expect a bigger patch would be needed for that. If not, what exactly are the semantics? Thanks, NeilBrown
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