mds: make max file recovers configurable

Signed-off-by: Sage Weil <sage@redhat.com>
mds: change mds_max_file_recover from 5 -> 32

These are reasonably cheap operations (stat) and we should be too worried
about queueing up a bunch of them.

Ideally this sort of thing would magically tune to the throughput we can
get from the cluster, but until then, let's choose a default that works for
more users.

Signed-off-by: Sage Weil <sage@redhat.com>
mds/RecoveryQueue: add method to prioritize a file recovery; fix logging

Add a prioritize() method to make file recovery start immediately for the
given inode.  Note that this doesn't respect the max recovery limit: if
someone stats it, they are blocking, and we start the recovery immediately.

Also fix up the dout logging a bit so that everything is prefixed
consistently.

Signed-off-by: Sage Weil <sage@redhat.com>
mds/Locker: prioritize file recovery on rd/wr/x lock

If someone specifically touches the file lock, prioritize recovery for this
file.

Signed-off-by: Sage Weil <sage@redhat.com>
mds/Locker: if a client asks for file caps, prioritize file recovery

This normally happens when a process opens the file.  Prioritize in that
case.

Signed-off-by: Sage Weil <sage@redhat.com>