On Wed, 2024-02-07 at 14:21 +0000, Trond Myklebust wrote: > On Wed, 2024-02-07 at 08:34 -0500, Jeff Layton wrote: > > I've started work on a patchset to add support for directory > > delegations > > to the Linux kernel client and server. It's still too rough to post > > at > > this point, and for now, I'm just cobbling in a ioctl to drive it. > > > > As I started working on some of the client bits, however, I realized > > that I don't really have a clear picture as to when the client should > > request a delegation on a directory. It seems like there are a lot of > > things we could do: > > > > One idea: request one on an initial directory readdir. So maybe when > > the > > offset is 0 and we don't have a dir delegation already, do: > > > > PUTFH:GET_DIR_DELEGATION:READDIR > > > > Or, maybe just do it on any readdir when we haven't requested one in > > a > > little while? > > > > We could also do one on every lookup, when we expect that the result > > will be a directory. I'm not sure if LOOKUP_DIRECTORY would be a > > sufficient indicator or if we'd need the vfs to indicate that with a > > new > > flag. > > > > Would we also want to request one after a mkdir? > > > > PUTFH:CREATE:GET_DIR_DELEGATION:GETFH:GET_DIR_DELEGATION:... > > > > Assuming we can get this all working, what should drive the client to > > issues GET_DIR_DELEGATION ops? > > As far as I'm concerned, the main case to be made for directory > delegations in the client is for reducing the number of revalidations > on said directory, particularly during path lookups. > i.e. the goal is to eliminate the need to constantly poll the directory > change attribute, and to eliminate the need to constantly revalidate > the dentries (and negative dentries!) contained in the directory after > a change. > > Perhaps that means we should focus on adding a request for a directory > delegation to the function nfs_lookup_revalidate() since that would > seem to indicate that we're going through the same directory multiple > times? The other call site to consider would be nfs_check_verifier(). > Sounds good. I'm not nearly at the point where I'm modifying client behavior yet, but I'll plan to try wiring it up in the revalidate codepaths first. -- Jeff Layton <jlayton@xxxxxxxxxx>
