Commit 60aa6564 authored by NeilBrown's avatar NeilBrown Committed by Chuck Lever
Browse files

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: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
parent 601c8cb3

fs/nfsd/nfs4state.c

+32 −5
Original line number Diff line number Diff line
@@ -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: