[PATCH 4/6] nfsd: allocate new session-based DRC slots on demand.

NeilBrown
2024-11-19T00:50:09Z

If a client ever uses the highest available slot for a given session,
attempt to allocate another slot so there is room for the client to use
more slots 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.

We would expect to stablise with one more slot available than the client
actually uses.

Now that we grow the slot table on demand we can start with a smaller
allocation. Define NFSD_MAX_INITIAL_SLOTS and allocate at most that
many when session is created.

Signed-off-by: NeilBrown <neilb@suse.de>
---
fs/nfsd/nfs4state.c | 32 ++++++++++++++++++++++++++------
fs/nfsd/state.h | 2 ++
2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 31ff9f92a895..fb522165b376 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1956,7 +1956,7 @@ static struct nfsd4_session *alloc_session(struct nfsd4_channel_attrs *fattrs,
if (!slot || xa_is_err(xa_store(&new->se_slots, 0, slot, GFP_KERNEL)))
goto out_free;

- for (i = 1; i < numslots; i++) {
+ for (i = 1; i < numslots && i < NFSD_MAX_INITIAL_SLOTS; i++) {
slot = kzalloc(slotsize, GFP_KERNEL | __GFP_NORETRY);
if (!slot)
break;
@@ -4248,11 +4248,6 @@ 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);
@@ -4302,6 +4297,31 @@ 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 one.
+ */
+ if (seq->slotid == session->se_fchannel.maxreqs - 1 &&
+ session->se_fchannel.maxreqs < NFSD_MAX_SLOTS_PER_SESSION) {
+ int s = session->se_fchannel.maxreqs;
+
+ /*
+ * GFP_NOWAIT is a low-priority non-blocking allocation
+ * which can be used under client_lock and only succeeds
+ * if there is plenty of memory.
+ * Use GFP_ATOMIC which is higher priority for xa_store()
+ * so we are less likely to waste the effort of the first
+ * allocation.
+ */
+ slot = kzalloc(slot_bytes(&session->se_fchannel), GFP_NOWAIT);
+ if (slot && !xa_is_err(xa_store(&session->se_slots, s, slot,
+ GFP_ATOMIC)))
+ session->se_fchannel.maxreqs += 1;
+ else
+ kfree(slot);
+ }
+ seq->maxslots = session->se_fchannel.maxreqs;
+
out:
switch (clp->cl_cb_state) {
case NFSD4_CB_DOWN:
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index e97626916a68..a14a823670e9 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -249,6 +249,8 @@ static inline struct nfs4_delegation *delegstateid(struct nfs4_stid *s)
* get good throughput on high-latency servers.
*/
#define NFSD_MAX_SLOTS_PER_SESSION 2048
+/* Maximum number of slots per session to allocate for CREATE_SESSION */
+#define NFSD_MAX_INITIAL_SLOTS 32
/* Maximum session per slot cache size */
#define NFSD_SLOT_CACHE_SIZE 2048
/* Maximum number of NFSD_SLOT_CACHE_SIZE slots per session */
--
2.47.0