nfsd: allocate new session-based DRC slots on demand.

If a client ever uses the highest available slot for a given session,
attempt to allocate more slots so there is room for the client to use
them if wanted.  GFP_NOWAIT is used so if there is not plenty of
free memory, failure is expected - which is what we want.  It also
allows the allocation while holding a spinlock.

Each time we increase the number of slots by 20% (rounded up).  This
allows fairly quick growth while avoiding excessive over-shoot.

We would expect to stablise with around 10% more slots available than
the client actually uses.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index bdfe791b02f159ea15f5bc622fe84a2cdd498680..fcc0153b6b90a6c910ccd3dd3e09e36b64749680 100644 (file)
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -4235,11 +4235,6 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
        slot = xa_load(&session->se_slots, seq->slotid);
        dprintk("%s: slotid %d\n", __func__, seq->slotid);
 
-       /* We do not negotiate the number of slots yet, so set the
-        * maxslots to the session maxreqs which is used to encode
-        * sr_highest_slotid and the sr_target_slot id to maxslots */
-       seq->maxslots = session->se_fchannel.maxreqs;
-
        trace_nfsd_slot_seqid_sequence(clp, seq, slot);
        status = check_slot_seqid(seq->seqid, slot->sl_seqid,
                                        slot->sl_flags & NFSD4_SLOT_INUSE);
@@ -4289,6 +4284,38 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
        cstate->session = session;
        cstate->clp = clp;
 
+       /*
+        * If the client ever uses the highest available slot,
+        * gently try to allocate another 20%.  This allows
+        * fairly quick growth without grossly over-shooting what
+        * the client might use.
+        */
+       if (seq->slotid == session->se_fchannel.maxreqs - 1 &&
+           session->se_fchannel.maxreqs < NFSD_MAX_SLOTS_PER_SESSION) {
+               int s = session->se_fchannel.maxreqs;
+               int cnt = DIV_ROUND_UP(s, 5);
+
+               do {
+                       /*
+                        * GFP_NOWAIT both allows allocation under a
+                        * spinlock, and only succeeds if there is
+                        * plenty of memory.
+                        */
+                       slot = kzalloc(slot_bytes(&session->se_fchannel),
+                                      GFP_NOWAIT);
+                       if (slot &&
+                           !xa_is_err(xa_store(&session->se_slots, s, slot,
+                                               GFP_NOWAIT))) {
+                               s += 1;
+                               session->se_fchannel.maxreqs = s;
+                       } else {
+                               kfree(slot);
+                               slot = NULL;
+                       }
+               } while (slot && --cnt > 0);
+       }
+       seq->maxslots = session->se_fchannel.maxreqs;
+
 out:
        switch (clp->cl_cb_state) {
        case NFSD4_CB_DOWN: