• David Howells's avatar
    afs: Overhaul the callback handling · c435ee34
    David Howells authored
    Overhaul the AFS callback handling by the following means:
     (1) Don't give up callback promises on vnodes that we are no longer using,
         rather let them just expire on the server or let the server break
         them.  This is actually more efficient for the server as the callback
         lookup is expensive if there are lots of extant callbacks.
     (2) Only give up the callback promises we have from a server when the
         server record is destroyed.  Then we can just give up *all* the
         callback promises on it in one go.
     (3) Servers can end up being shared between cells if cells are aliased, so
         don't add all the vnodes being backed by a particular server into a
         big FID-indexed tree on that server as there may be duplicates.
         Instead have each volume instance (~= superblock) register an interest
         in a server as it starts to make use of it and use this to allow the
         processor for callbacks from the server to find the superblock and
         thence the inode corresponding to the FID being broken by means of
     (4) Rather than iterating over the entire callback list when a mass-break
         comes in from the server, maintain a counter of mass-breaks in
         afs_server (cb_seq) and make afs_validate() check it against the copy
         in afs_vnode.
         It would be nice not to have to take a read_lock whilst doing this,
         but that's tricky without using RCU.
     (5) Save a ref on the fileserver we're using for a call in the afs_call
         struct so that we can access its cb_s_break during call decoding.
     (6) Write-lock around callback and status storage in a vnode and read-lock
         around getattr so that we don't see the status mid-update.
    This has the following consequences:
     (1) Data invalidation isn't seen until someone calls afs_validate() on a
         vnode.  Unfortunately, we need to use a key to query the server, but
         getting one from a background thread is tricky without caching loads
         of keys all over the place.
     (2) Mass invalidation isn't seen until someone calls afs_validate().
     (3) Callback breaking is going to hit the inode_hash_lock quite a bit.
         Could this be replaced with rcu_read_lock() since inodes are destroyed
         under RCU conditions.
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
afs_fs.h 2.56 KB