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

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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>
This commit is contained in:
NeilBrown 2024-12-12 08:47:07 +11:00 • committed by Chuck Lever
parent 601c8cb349
commit 60aa656431
1 changed files with 32 additions and 5 deletions
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37
fs/nfsd/nfs4state.c
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@ -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: