On Tue, 2022-08-30 at 14:32 -0400, J. Bruce Fields wrote: > On Tue, Aug 30, 2022 at 01:02:50PM -0400, Jeff Layton wrote: > > The fact that NFS kept this more loosely-defined is what allowed us to > > elide some of the i_version bumps and regain a fair bit of performance > > for local filesystems [1]. If the change attribute had been more > > strictly defined like you mention, then that particular optimization > > would not have been possible. > > > > This sort of thing is why I'm a fan of not defining this any more > > strictly than we require. Later on, maybe we'll come up with a way for > > filesystems to advertise that they can offer stronger guarantees. > > Yeah, the afs change-attribute-as-counter thing seems ambitious--I > wouldn't even know how to define what exactly you're counting. > > My one question is whether it'd be worth just defining the thing as > *increasing*. That's a lower bar. > That's a very good question. One could argue that NFSv4 sort of requires that for write delegations anyway. All of the existing implementations that I know of do this, so that wouldn't rule any of them out. I'm not opposed to adding that constraint. Let me think on it a bit more. > (Though admittedly we don't quite manage it now--see again 1631087ba872 > "Revert "nfsd4: support change_attr_type attribute"".) > Factoring the ctime into the change attr seems wrong, since a clock jump could make it go backward. Do you remember what drove that change (see 630458e730b8) ? It seems like if the i_version were to go backward, then the ctime probably would too, and you'd still see a duplicate change attr. -- Jeff Layton <jlayton@xxxxxxxxxx>
