[PATCH v5 0/5] sunrpc: hardcode pool_mode to pernode, remove other modes

[PATCH v5 0/5] sunrpc: hardcode pool_mode to pernode, remove other modes

[Jeff Layton]

This has a few small fixes and comment cleanups and also implements
Neil's suggestion to remove serv.sv_nrpools:

Patches #1 and #3 address what is a shortcoming of the existing code --
namely that the server can be configured to schedule RPCs to pools with
no threads in them.

The first patch addresses this problem: if the chosen pool has no
threads, then choose another that does.

The third patch tries to prevent this situation in the
auto-thread-placement case by ensuring that each populated node has at
least one thread.

The last two patches implement Neil's suggestion to eliminate
serv.sv_nrpools. This has the side effect of getting the modulus out of
the svc_pool_for_cpu() hotpath as well.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
Changes in v5:
- Expand patch to eliminate modulus to also eliminate serv.sv_nrpools field
- Revised comments in svc_pool_for_cpu()
- Link to v4: https://lore.kernel.org/r/20260701-sunrpc-pool-mode-v4-0-b3d867e4c8f9@kernel.org

Changes in v4:
- Drop 5/4 RCU patch
- Only let pooled services consult the map
- Comment and commit log fixes
- Link to v3: https://lore.kernel.org/r/20260629-sunrpc-pool-mode-v3-0-d92676606dfd@kernel.org

Changes in v3:
- Add patch to ensure that we don't route requests to empty pools
- When auto-distributing threads, always create at least one thread per populated pool
- Use sysfs_match_string for the module parameter
- Reword deprecation printk to be more vague about removal
- Explicitly set m_count == 0 in svc_pool_map_get()
- Optimize svc_pool_for_cpu() by eliminating modulus ops
- Link to v2: https://lore.kernel.org/r/20260625-sunrpc-pool-mode-v2-1-4f512b6e1ee8@kernel.org

Changes in v2:
- Accept any previously-accepted setting for pool_mode
- Link to v1: https://lore.kernel.org/r/20260423-sunrpc-pool-mode-v1-1-b7f20e35749b@kernel.org

---
Jeff Layton (5):
      sunrpc: route to a populated pool in svc_pool_for_cpu()
      sunrpc: hardcode pool_mode to pernode, remove other modes
      sunrpc: guarantee a thread per pool when auto-distributing
      sunrpc: tear down pool counters before dropping the pool map reference
      sunrpc: derive the pool count instead of caching it in sv_nrpools

 Documentation/admin-guide/kernel-parameters.txt |  20 +-
 fs/nfsd/nfsctl.c                                |   2 +-
 fs/nfsd/nfssvc.c                                |  10 +-
 include/linux/sunrpc/svc.h                      |   2 +-
 net/sunrpc/svc.c                                | 355 +++++++++---------------
 net/sunrpc/svc_xprt.c                           |   6 +-
 6 files changed, 152 insertions(+), 243 deletions(-)
---
base-commit: ee6ae4a6bf3565b880dfb420017337475dfbc9ea
change-id: 20260423-sunrpc-pool-mode-3e6b56320dc4

Best regards,
-- 
Jeff Layton <jlayton@kernel.org>

[PATCH v5 1/5] sunrpc: route to a populated pool in svc_pool_for_cpu()

[Jeff Layton]

svc_set_num_threads() spreads the requested threads evenly across the
service's pools (base = nrservs / sv_nrpools).  When a service runs
fewer threads than it has pools -- e.g. an nfsd configured with fewer
threads than the host has NUMA nodes while running in "pernode" or
"percpu" mode -- the trailing pools are left with no threads at all.

svc_xprt_enqueue() selects a pool from the CPU servicing the transport,
queues the transport on that pool's sp_xprts, and only wakes a thread
from the same pool.  Each thread services exclusively its own pool, so a
transport that lands on a threadless pool is enqueued on sp_xprts and
never picked up: the connection hangs indefinitely.

Have svc_pool_for_cpu() skip pools that currently have no threads,
falling back to the next populated pool.  This trades NUMA locality for
a guarantee that the work is actually serviced.  sp_nrthreads is only
updated under the service mutex; the lockless read here is a best-effort
routing hint, so annotate it with data_race().

Fixes: bfd241600a3b ("[PATCH] knfsd: make rpc threads pools numa aware")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 net/sunrpc/svc.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index dd80a2eaaa74..fa8056fb0b4d 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -402,6 +402,7 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
 	struct svc_pool_map *m = &svc_pool_map;
 	int cpu = raw_smp_processor_id();
 	unsigned int pidx = 0;
+	unsigned int i;
 
 	if (serv->sv_nrpools <= 1)
 		return serv->sv_pools;
@@ -414,8 +415,34 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
 		pidx = m->to_pool[cpu_to_node(cpu)];
 		break;
 	}
+	pidx %= serv->sv_nrpools;
+
+	/*
+	 * It's possible to have a pool with no threads. Userland can just set
+	 * things up this way directly. Also, when threads are autodistributed
+	 * they are spread evenly across the pools, but when there are fewer
+	 * threads than pools some pools can end up with none.
+	 *
+	 * A transport enqueued on a threadless pool would never be picked up,
+	 * since each thread only services its own pool. Fall back to the next
+	 * populated pool, trading NUMA locality for a guarantee that the
+	 * transport is serviced.
+	 */
+	for (i = 0; i < serv->sv_nrpools; i++) {
+		struct svc_pool *pool = &serv->sv_pools[pidx];
+
+		/* This is set under the sp_mutex and rarely ever changes. A
+		 * data race here is harmless.
+		 */
+		if (data_race(pool->sp_nrthreads))
+			return pool;
+
+		if (++pidx >= serv->sv_nrpools)
+			pidx = 0;
+	}
 
-	return &serv->sv_pools[pidx % serv->sv_nrpools];
+	/* No pool has any threads; nothing can service the transport. */
+	return &serv->sv_pools[pidx];
 }
 
 static int svc_rpcb_setup(struct svc_serv *serv, struct net *net)

-- 
2.55.0

[PATCH v5 2/5] sunrpc: hardcode pool_mode to pernode, remove other modes

[Jeff Layton]

The SVC_POOL_AUTO/GLOBAL/PERCPU/PERNODE pool mode selection machinery
was added when NUMA was new and the right default was unclear.  The
default has always been "global" (a single pool for the whole service);
the other modes were only used when an admin explicitly set the
pool_mode parameter or asked for "auto", which then picked a mode from
the host topology.  Today, pernode is the right choice everywhere:

- On multi-NUMA hosts, it gives one pool per node with proper thread
  affinity and NUMA-local memory allocation.
- On single-node hosts, pernode degenerates to exactly one pool,
  identical to the old "global" mode -- svc_pool_for_cpu() short-
  circuits when sv_nrpools <= 1, no CPU affinity is set, and memory
  is allocated from the single node.

The percpu mode (one pool per CPU) created excessive pools relative to
the number of threads most deployments run, and was only auto-selected
in a narrow case (single node, >2 CPUs).

Note that this changes the default behaviour on multi-NUMA hosts: a
service that previously ran with a single global pool now gets one pool
per NUMA node by default.  This in turn means a host running fewer
threads than it has NUMA nodes can end up with pools that have no
threads.  svc_pool_for_cpu() already falls back to a populated pool in
that case, so transports are still serviced.

Remove the SVC_POOL_* enum, mode selection heuristic,
svc_pool_map_init_percpu(), and all mode-based switch statements.
Simplify pool map functions to always use the pernode path.  If pool
map allocation fails, svc_pool_map_get() now returns 0 and service
creation fails, rather than silently falling back to a single global
pool.

With the mode check gone, svc_pool_map_get_node() would dereference the
shared pool_to[] for every service that starts a thread.  Only services
created via svc_create_pooled() hold a map reference that keeps that
array allocated, so gate the lookup in svc_new_thread() on sv_is_pooled:
unpooled services (e.g. lockd, the NFS callback) use NUMA_NO_NODE and
never consult the map.  The kmalloc_node() callers in
svc_prepare_thread() already accept NUMA_NO_NODE, but __folio_alloc_node()
requires a valid node id, so resolve NUMA_NO_NODE to numa_mem_id() for
the scratch folio allocation.

The module parameter and netlink interfaces are preserved for backward
compatibility:
- Writing any of the four documented mode names still succeeds silently
- Reading always returns "pernode"
- Writing to the module parameter emits a deprecation notice

Update Documentation/admin-guide/kernel-parameters.txt to mark the
pool_mode parameter deprecated and describe the new behaviour.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  20 +-
 net/sunrpc/svc.c                                | 265 ++++++------------------
 2 files changed, 65 insertions(+), 220 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b5493a7f8f22..441b78867478 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7441,19 +7441,13 @@ Kernel parameters
 
 	sunrpc.pool_mode=
 			[NFS]
-			Control how the NFS server code allocates CPUs to
-			service thread pools.  Depending on how many NICs
-			you have and where their interrupts are bound, this
-			option will affect which CPUs will do NFS serving.
-			Note: this parameter cannot be changed while the
-			NFS server is running.
-
-			auto	    the server chooses an appropriate mode
-				    automatically using heuristics
-			global	    a single global pool contains all CPUs
-			percpu	    one pool for each CPU
-			pernode	    one pool for each NUMA node (equivalent
-				    to global on non-NUMA machines)
+			Deprecated.  The NFS server now always uses one
+			service thread pool per NUMA node (equivalent to a
+			single global pool on non-NUMA machines).  All of
+			the previously accepted values (auto, global,
+			percpu, pernode) are still accepted for backward
+			compatibility but are ignored: the mode is always
+			pernode, and reads always return "pernode".
 
 	sunrpc.tcp_slot_table_entries=
 	sunrpc.udp_slot_table_entries=
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index fa8056fb0b4d..b942845f82a3 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -38,82 +38,36 @@
 
 static void svc_unregister(const struct svc_serv *serv, struct net *net);
 
-#define SVC_POOL_DEFAULT	SVC_POOL_GLOBAL
-
 /*
- * Mode for mapping cpus to pools.
- */
-enum {
-	SVC_POOL_AUTO = -1,	/* choose one of the others */
-	SVC_POOL_GLOBAL,	/* no mapping, just a single global pool
-				 * (legacy & UP mode) */
-	SVC_POOL_PERCPU,	/* one pool per cpu */
-	SVC_POOL_PERNODE	/* one pool per numa node */
-};
-
-/*
- * Structure for mapping cpus to pools and vice versa.
+ * Structure for mapping nodes to pools and vice versa.
  * Setup once during sunrpc initialisation.
  */
 
 struct svc_pool_map {
 	int count;			/* How many svc_servs use us */
-	int mode;			/* Note: int not enum to avoid
-					 * warnings about "enumeration value
-					 * not handled in switch" */
 	unsigned int npools;
-	unsigned int *pool_to;		/* maps pool id to cpu or node */
-	unsigned int *to_pool;		/* maps cpu or node to pool id */
+	unsigned int *pool_to;		/* maps pool id to node */
+	unsigned int *to_pool;		/* maps node to pool id */
 };
 
-static struct svc_pool_map svc_pool_map = {
-	.mode = SVC_POOL_DEFAULT
-};
+static struct svc_pool_map svc_pool_map;
 
 static DEFINE_MUTEX(svc_pool_map_mutex);/* protects svc_pool_map.count only */
 
-static int
-__param_set_pool_mode(const char *val, struct svc_pool_map *m)
-{
-	int err, mode;
-
-	mutex_lock(&svc_pool_map_mutex);
-
-	err = 0;
-	if (!strncmp(val, "auto", 4))
-		mode = SVC_POOL_AUTO;
-	else if (!strncmp(val, "global", 6))
-		mode = SVC_POOL_GLOBAL;
-	else if (!strncmp(val, "percpu", 6))
-		mode = SVC_POOL_PERCPU;
-	else if (!strncmp(val, "pernode", 7))
-		mode = SVC_POOL_PERNODE;
-	else
-		err = -EINVAL;
-
-	if (err)
-		goto out;
-
-	if (m->count == 0)
-		m->mode = mode;
-	else if (mode != m->mode)
-		err = -EBUSY;
-out:
-	mutex_unlock(&svc_pool_map_mutex);
-	return err;
-}
-
-static int
-param_set_pool_mode(const char *val, const struct kernel_param *kp)
-{
-	struct svc_pool_map *m = kp->arg;
-
-	return __param_set_pool_mode(val, m);
-}
+/*
+ * Pool modes that were historically accepted. They no longer select
+ * anything: the pool mode is always pernode. The names are retained
+ * only so that writing a previously-valid value still succeeds.
+ */
+static const char * const pool_mode_names[] = {
+	"auto", "global", "percpu", "pernode",
+};
 
 int sunrpc_set_pool_mode(const char *val)
 {
-	return __param_set_pool_mode(val, &svc_pool_map);
+	int idx = sysfs_match_string(pool_mode_names, val);
+
+	return idx < 0 ? idx : 0;
 }
 EXPORT_SYMBOL(sunrpc_set_pool_mode);
 
@@ -122,84 +76,32 @@ EXPORT_SYMBOL(sunrpc_set_pool_mode);
  * @buf: where to write the current pool_mode
  * @size: size of @buf
  *
- * Grab the current pool_mode from the svc_pool_map and write
- * the resulting string to @buf. Returns the number of characters
+ * Write the pool_mode string to @buf. Returns the number of characters
  * written to @buf (a'la snprintf()).
  */
 int
 sunrpc_get_pool_mode(char *buf, size_t size)
 {
-	struct svc_pool_map *m = &svc_pool_map;
-
-	switch (m->mode)
-	{
-	case SVC_POOL_AUTO:
-		return snprintf(buf, size, "auto");
-	case SVC_POOL_GLOBAL:
-		return snprintf(buf, size, "global");
-	case SVC_POOL_PERCPU:
-		return snprintf(buf, size, "percpu");
-	case SVC_POOL_PERNODE:
-		return snprintf(buf, size, "pernode");
-	default:
-		return snprintf(buf, size, "%d", m->mode);
-	}
+	return snprintf(buf, size, "pernode");
 }
 EXPORT_SYMBOL(sunrpc_get_pool_mode);
 
 static int
-param_get_pool_mode(char *buf, const struct kernel_param *kp)
+param_set_pool_mode(const char *val, const struct kernel_param *kp)
 {
-	char str[16];
-	int len;
-
-	len = sunrpc_get_pool_mode(str, ARRAY_SIZE(str));
-
-	/* Ensure we have room for newline and NUL */
-	len = min_t(int, len, ARRAY_SIZE(str) - 2);
-
-	/* tack on the newline */
-	str[len] = '\n';
-	str[len + 1] = '\0';
-
-	return sysfs_emit(buf, "%s", str);
+	pr_notice_once("sunrpc: the pool_mode module parameter is deprecated and no longer has any effect; the pool mode is always 'pernode'\n");
+	return sunrpc_set_pool_mode(val);
 }
 
-module_param_call(pool_mode, param_set_pool_mode, param_get_pool_mode,
-		  &svc_pool_map, 0644);
-
-/*
- * Detect best pool mapping mode heuristically,
- * according to the machine's topology.
- */
 static int
-svc_pool_map_choose_mode(void)
+param_get_pool_mode(char *buf, const struct kernel_param *kp)
 {
-	unsigned int node;
-
-	if (nr_online_nodes > 1) {
-		/*
-		 * Actually have multiple NUMA nodes,
-		 * so split pools on NUMA node boundaries
-		 */
-		return SVC_POOL_PERNODE;
-	}
-
-	node = first_online_node;
-	if (nr_cpus_node(node) > 2) {
-		/*
-		 * Non-trivial SMP, or CONFIG_NUMA on
-		 * non-NUMA hardware, e.g. with a generic
-		 * x86_64 kernel on Xeons.  In this case we
-		 * want to divide the pools on cpu boundaries.
-		 */
-		return SVC_POOL_PERCPU;
-	}
-
-	/* default: one global pool */
-	return SVC_POOL_GLOBAL;
+	return sysfs_emit(buf, "pernode\n");
 }
 
+module_param_call(pool_mode, param_set_pool_mode, param_get_pool_mode,
+		  NULL, 0644);
+
 /*
  * Allocate the to_pool[] and pool_to[] arrays.
  * Returns 0 on success or an errno.
@@ -224,35 +126,7 @@ svc_pool_map_alloc_arrays(struct svc_pool_map *m, unsigned int maxpools)
 }
 
 /*
- * Initialise the pool map for SVC_POOL_PERCPU mode.
- * Returns number of pools or <0 on error.
- */
-static int
-svc_pool_map_init_percpu(struct svc_pool_map *m)
-{
-	unsigned int maxpools = nr_cpu_ids;
-	unsigned int pidx = 0;
-	unsigned int cpu;
-	int err;
-
-	err = svc_pool_map_alloc_arrays(m, maxpools);
-	if (err)
-		return err;
-
-	for_each_online_cpu(cpu) {
-		BUG_ON(pidx >= maxpools);
-		m->to_pool[cpu] = pidx;
-		m->pool_to[pidx] = cpu;
-		pidx++;
-	}
-	/* cpus brought online later all get mapped to pool0, sorry */
-
-	return pidx;
-};
-
-
-/*
- * Initialise the pool map for SVC_POOL_PERNODE mode.
+ * Initialise the pool map for one pool per NUMA node.
  * Returns number of pools or <0 on error.
  */
 static int
@@ -281,17 +155,16 @@ svc_pool_map_init_pernode(struct svc_pool_map *m)
 
 
 /*
- * Add a reference to the global map of cpus to pools (and
+ * Add a reference to the global map of nodes to pools (and
  * vice versa) if pools are in use.
  * Initialise the map if we're the first user.
- * Returns the number of pools. If this is '1', no reference
- * was taken.
+ * Returns the number of pools, or 0 on failure.
  */
 static unsigned int
 svc_pool_map_get(void)
 {
 	struct svc_pool_map *m = &svc_pool_map;
-	int npools = -1;
+	int npools;
 
 	mutex_lock(&svc_pool_map_mutex);
 	if (m->count++) {
@@ -299,22 +172,11 @@ svc_pool_map_get(void)
 		return m->npools;
 	}
 
-	if (m->mode == SVC_POOL_AUTO)
-		m->mode = svc_pool_map_choose_mode();
-
-	switch (m->mode) {
-	case SVC_POOL_PERCPU:
-		npools = svc_pool_map_init_percpu(m);
-		break;
-	case SVC_POOL_PERNODE:
-		npools = svc_pool_map_init_pernode(m);
-		break;
-	}
-
+	npools = svc_pool_map_init_pernode(m);
 	if (npools <= 0) {
-		/* default, or memory allocation failure */
-		npools = 1;
-		m->mode = SVC_POOL_GLOBAL;
+		m->count = 0;
+		mutex_unlock(&svc_pool_map_mutex);
+		return 0;
 	}
 	m->npools = npools;
 	mutex_unlock(&svc_pool_map_mutex);
@@ -322,7 +184,7 @@ svc_pool_map_get(void)
 }
 
 /*
- * Drop a reference to the global map of cpus to pools.
+ * Drop a reference to the global map of nodes to pools.
  * When the last reference is dropped, the map data is
  * freed; this allows the sysadmin to change the pool.
  */
@@ -346,14 +208,11 @@ static int svc_pool_map_get_node(unsigned int pidx)
 {
 	const struct svc_pool_map *m = &svc_pool_map;
 
-	if (m->count) {
-		if (m->mode == SVC_POOL_PERCPU)
-			return cpu_to_node(m->pool_to[pidx]);
-		if (m->mode == SVC_POOL_PERNODE)
-			return m->pool_to[pidx];
-	}
+	if (m->count)
+		return m->pool_to[pidx];
 	return numa_mem_id();
 }
+
 /*
  * Set the given thread's cpus_allowed mask so that it
  * will only run on cpus in the given pool.
@@ -372,27 +231,15 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
 	if (m->count == 0)
 		return;
 
-	switch (m->mode) {
-	case SVC_POOL_PERCPU:
-	{
-		set_cpus_allowed_ptr(task, cpumask_of(node));
-		break;
-	}
-	case SVC_POOL_PERNODE:
-	{
-		set_cpus_allowed_ptr(task, cpumask_of_node(node));
-		break;
-	}
-	}
+	set_cpus_allowed_ptr(task, cpumask_of_node(node));
 }
 
 /**
  * svc_pool_for_cpu - Select pool to run a thread on this cpu
  * @serv: An RPC service
  *
- * Use the active CPU and the svc_pool_map's mode setting to
- * select the svc thread pool to use. Once initialized, the
- * svc_pool_map does not change.
+ * Use the active CPU and the svc_pool_map to select the svc thread
+ * pool to use. Once initialized, the svc_pool_map does not change.
  *
  * Return value:
  *   A pointer to an svc_pool
@@ -400,22 +247,12 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
 struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
 {
 	struct svc_pool_map *m = &svc_pool_map;
-	int cpu = raw_smp_processor_id();
-	unsigned int pidx = 0;
-	unsigned int i;
+	unsigned int pidx, i;
 
 	if (serv->sv_nrpools <= 1)
 		return serv->sv_pools;
 
-	switch (m->mode) {
-	case SVC_POOL_PERCPU:
-		pidx = m->to_pool[cpu];
-		break;
-	case SVC_POOL_PERNODE:
-		pidx = m->to_pool[cpu_to_node(cpu)];
-		break;
-	}
-	pidx %= serv->sv_nrpools;
+	pidx = m->to_pool[cpu_to_node(raw_smp_processor_id())] % serv->sv_nrpools;
 
 	/*
 	 * It's possible to have a pool with no threads. Userland can just set
@@ -644,6 +481,9 @@ struct svc_serv *svc_create_pooled(struct svc_program *prog,
 	struct svc_serv *serv;
 	unsigned int npools = svc_pool_map_get();
 
+	if (!npools)
+		return NULL;
+
 	serv = __svc_create(prog, nprogs, stats, bufsize, npools, threadfn);
 	if (!serv)
 		goto out_err;
@@ -778,7 +618,10 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node)
 	rqstp->rq_server = serv;
 	rqstp->rq_pool = pool;
 
-	rqstp->rq_scratch_folio = __folio_alloc_node(GFP_KERNEL, 0, node);
+	/* __folio_alloc_node() rejects NUMA_NO_NODE; let it pick for us */
+	rqstp->rq_scratch_folio =
+		__folio_alloc_node(GFP_KERNEL, 0,
+				   node == NUMA_NO_NODE ? numa_mem_id() : node);
 	if (!rqstp->rq_scratch_folio)
 		goto out_enomem;
 
@@ -867,7 +710,15 @@ int svc_new_thread(struct svc_serv *serv, struct svc_pool *pool)
 	int node;
 	int err = 0;
 
-	node = svc_pool_map_get_node(pool->sp_id);
+	/*
+	 * Only pooled services hold a reference to the pool map, so only they
+	 * may consult it. Unpooled services (e.g. lockd, the NFS callback)
+	 * leave placement to the allocator.
+	 */
+	if (serv->sv_is_pooled)
+		node = svc_pool_map_get_node(pool->sp_id);
+	else
+		node = NUMA_NO_NODE;
 
 	rqstp = svc_prepare_thread(serv, pool, node);
 	if (!rqstp)

-- 
2.55.0

[PATCH v5 3/5] sunrpc: guarantee a thread per pool when auto-distributing

[Jeff Layton]

svc_set_num_threads() spreads the requested thread count evenly across
the service's pools. In pernode mode each pool maps to a NUMA node, and
svc_pool_for_cpu() steers an incoming transport to the pool for the node
it arrived on. When fewer threads than pools are requested, even
distribution leaves some pools empty, and a transport steered to an
empty pool has no thread to service it.

Floor each pool at one thread when auto-distributing a non-zero count,
so no pool is left empty. Every pool maps to a node that had CPUs when
the pool map was built (svc_pool_map_init_pernode() only creates pools
for nodes returned by for_each_node_with_cpus()), so there is no pool
that should be left threadless. The resulting total may exceed the
requested count. This only affects the auto-distribute path (a
single-value array, i.e. svc_set_num_threads()); callers that set
per-pool counts explicitly via svc_set_pool_threads() are unchanged and
may still set a pool to zero.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: NeilBrown <neil@brown.name>
---
 net/sunrpc/svc.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index b942845f82a3..2d1cdf55c561 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -840,6 +840,12 @@ EXPORT_SYMBOL_GPL(svc_set_pool_threads);
  * are multiple pools then the new threads or victims will be distributed
  * evenly among them.
  *
+ * When @nrservs is non-zero but smaller than the number of pools, even
+ * distribution would leave some pools empty. Since each pool maps to a
+ * NUMA node and only services transports steered to that node, every
+ * pool is instead guaranteed at least one thread. The resulting total
+ * may therefore exceed @nrservs.
+ *
  * Caller must ensure mutual exclusion between this and server startup or
  * shutdown.
  *
@@ -855,6 +861,16 @@ svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
 	unsigned int remain = nrservs % serv->sv_nrpools;
 	int i, err = 0;
 
+	/*
+	 * Don't let a pool sit empty while threads are being
+	 * auto-distributed: a transport steered to its node would have
+	 * nothing to service it. Every pool maps to a CPU-bearing node,
+	 * so hand each one a thread. This may push the total above
+	 * @nrservs.
+	 */
+	if (base == 0 && nrservs != 0)
+		remain = serv->sv_nrpools;
+
 	for (i = 0; i < serv->sv_nrpools; ++i) {
 		struct svc_pool *pool = &serv->sv_pools[i];
 		int threads = base;

-- 
2.55.0

[PATCH v5 4/5] sunrpc: tear down pool counters before dropping the pool map reference

[Jeff Layton]

svc_destroy() drops the service's reference to the global svc_pool_map
before iterating serv->sv_pools[] to destroy each pool's percpu counters.
That ordering happens to be fine today because the loop is bounded by the
per-service sv_nrpools field.

A following patch removes sv_nrpools and derives the pool count from the
pool map instead. svc_pool_map_put() zeroes svc_pool_map.npools when the
last reference is dropped, so a derived loop bound would read as zero for
the last pooled service and skip svc_pool_destroy_counters() entirely,
leaking the percpu counters (which remain linked on the global
percpu_counters list while the svc_serv is freed).

Reorder svc_destroy() to destroy the pool counters while the map is still
referenced, then drop the reference. No functional change.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 net/sunrpc/svc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 2d1cdf55c561..ece69cb0138a 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -520,14 +520,15 @@ svc_destroy(struct svc_serv **servp)
 
 	cache_clean_deferred(serv);
 
-	if (serv->sv_is_pooled)
-		svc_pool_map_put();
-
 	for (i = 0; i < serv->sv_nrpools; i++) {
 		struct svc_pool *pool = &serv->sv_pools[i];
 
 		svc_pool_destroy_counters(pool);
 	}
+
+	if (serv->sv_is_pooled)
+		svc_pool_map_put();
+
 	kfree(serv->sv_pools);
 	kfree(serv);
 }

-- 
2.55.0

[PATCH v5 5/5] sunrpc: derive the pool count instead of caching it in sv_nrpools

[Jeff Layton]

Now that the pool mode is always pernode, svc_serv.sv_nrpools is
redundant with sv_is_pooled: an unpooled service always has a single
pool, and a pooled service has svc_pool_map.npools pools (which is one on
a single-node host). sv_nrpools cannot distinguish an unpooled service
from a pooled service that happens to have one pool, so it is sv_nrpools,
not sv_is_pooled, that carries no unique information.

Replace the cached field with a svc_serv_nrpools() helper that derives
the count from sv_is_pooled and the pool map, and convert all readers to
it. svc_pool_map is file-local to svc.c, so export the helper for the
svc_xprt.c and nfsd callers.

Reading svc_pool_map.npools without svc_pool_map_mutex is safe: the
mutex protects only svc_pool_map.count, and npools is already read
locklessly in svc_pool_for_cpu().

A pooled service holds a map reference for its whole lifetime, so npools
is stable while any reader could observe it.  The hot path
(svc_pool_for_cpu()) already dereferences svc_pool_map for to_pool, and
npools shares that cacheline, so there is no new locking or coherence
cost.

__svc_create() keeps using its local npools argument for the sv_pools[]
allocation, since sv_is_pooled is not set until svc_create_pooled() has
returned from it.

Doing this also removes a modulus operation from svc_pool_for_cpu(),
which should make for more efficient RPC queueing.

Assisted-by: Claude:claude-opus-4-8
Suggested-by: NeilBrown <neilb@ownmail.net>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfsctl.c           |  2 +-
 fs/nfsd/nfssvc.c           | 10 ++++-----
 include/linux/sunrpc/svc.h |  2 +-
 net/sunrpc/svc.c           | 52 ++++++++++++++++++++++++++++++++--------------
 net/sunrpc/svc_xprt.c      |  6 +++---
 5 files changed, 46 insertions(+), 26 deletions(-)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index bc16fc7ca24f..0543e5bb842f 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1526,7 +1526,7 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
 
 	rcu_read_lock();
 
-	for (i = 0; i < nn->nfsd_serv->sv_nrpools; i++) {
+	for (i = 0; i < svc_serv_nrpools(nn->nfsd_serv); i++) {
 		struct svc_rqst *rqstp;
 		long thread_skip = 0;
 
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index a8ea4dbfa56b..2edf716ea022 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -655,7 +655,7 @@ int nfsd_nrpools(struct net *net)
 	if (nn->nfsd_serv == NULL)
 		return 0;
 	else
-		return nn->nfsd_serv->sv_nrpools;
+		return svc_serv_nrpools(nn->nfsd_serv);
 }
 
 int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
@@ -665,7 +665,7 @@ int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
 	int i;
 
 	if (serv)
-		for (i = 0; i < serv->sv_nrpools && i < n; i++)
+		for (i = 0; i < svc_serv_nrpools(serv) && i < n; i++)
 			nthreads[i] = serv->sv_pools[i].sp_nrthrmax;
 	return 0;
 }
@@ -699,8 +699,8 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 	if (n == 1)
 		return svc_set_num_threads(nn->nfsd_serv, nn->min_threads, nthreads[0]);
 
-	if (n > nn->nfsd_serv->sv_nrpools)
-		n = nn->nfsd_serv->sv_nrpools;
+	if (n > svc_serv_nrpools(nn->nfsd_serv))
+		n = svc_serv_nrpools(nn->nfsd_serv);
 
 	/* enforce a global maximum number of threads */
 	tot = 0;
@@ -731,7 +731,7 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 	}
 
 	/* Anything undefined in array is considered to be 0 */
-	for (i = n; i < nn->nfsd_serv->sv_nrpools; ++i) {
+	for (i = n; i < svc_serv_nrpools(nn->nfsd_serv); ++i) {
 		err = svc_set_pool_threads(nn->nfsd_serv,
 					   &nn->nfsd_serv->sv_pools[i],
 					   0, 0);
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 3a0152d926fb..3c885ab6ad41 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -85,7 +85,6 @@ struct svc_serv {
 
 	char *			sv_name;	/* service name */
 
-	unsigned int		sv_nrpools;	/* number of thread pools */
 	bool			sv_is_pooled;	/* is this a pooled service? */
 	struct svc_pool *	sv_pools;	/* array of thread pools */
 	int			(*sv_threadfn)(void *data);
@@ -480,6 +479,7 @@ void		   svc_wake_up(struct svc_serv *);
 void		   svc_reserve(struct svc_rqst *rqstp, int space);
 void		   svc_pool_wake_idle_thread(struct svc_pool *pool);
 struct svc_pool   *svc_pool_for_cpu(struct svc_serv *serv);
+unsigned int	   svc_serv_nrpools(const struct svc_serv *serv);
 char *		   svc_print_addr(struct svc_rqst *, char *, size_t);
 const char *	   svc_proc_name(const struct svc_rqst *rqstp);
 int		   svc_encode_result_payload(struct svc_rqst *rqstp,
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index ece69cb0138a..800514a14f17 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -224,7 +224,7 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
 	unsigned int node = m->pool_to[pidx];
 
 	/*
-	 * The caller checks for sv_nrpools > 1, which
+	 * The caller checks for more than one pool, which
 	 * implies that we've been initialized.
 	 */
 	WARN_ON_ONCE(m->count == 0);
@@ -234,6 +234,24 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
 	set_cpus_allowed_ptr(task, cpumask_of_node(node));
 }
 
+/**
+ * svc_serv_nrpools - number of thread pools backing a service
+ * @serv: An RPC service
+ *
+ * Pooled services all share the global svc_pool_map, so their pool count
+ * is svc_pool_map.npools. Unpooled services have a single pool. Reading
+ * npools without svc_pool_map_mutex is safe: a pooled service holds a map
+ * reference for its whole lifetime, so npools is stable once set.
+ *
+ * Return value:
+ *   The number of pools in @serv
+ */
+unsigned int svc_serv_nrpools(const struct svc_serv *serv)
+{
+	return serv->sv_is_pooled ? svc_pool_map.npools : 1;
+}
+EXPORT_SYMBOL_GPL(svc_serv_nrpools);
+
 /**
  * svc_pool_for_cpu - Select pool to run a thread on this cpu
  * @serv: An RPC service
@@ -247,12 +265,15 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
 struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
 {
 	struct svc_pool_map *m = &svc_pool_map;
+	unsigned int nrpools = svc_serv_nrpools(serv);
 	unsigned int pidx, i;
 
-	if (serv->sv_nrpools <= 1)
+	if (nrpools <= 1)
 		return serv->sv_pools;
 
-	pidx = m->to_pool[cpu_to_node(raw_smp_processor_id())] % serv->sv_nrpools;
+	pidx = m->to_pool[cpu_to_node(raw_smp_processor_id())];
+	if (pidx >= nrpools)
+		pidx = 0;
 
 	/*
 	 * It's possible to have a pool with no threads. Userland can just set
@@ -265,7 +286,7 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
 	 * populated pool, trading NUMA locality for a guarantee that the
 	 * transport is serviced.
 	 */
-	for (i = 0; i < serv->sv_nrpools; i++) {
+	for (i = 0; i < nrpools; i++) {
 		struct svc_pool *pool = &serv->sv_pools[pidx];
 
 		/* This is set under the sp_mutex and rarely ever changes. A
@@ -274,7 +295,7 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
 		if (data_race(pool->sp_nrthreads))
 			return pool;
 
-		if (++pidx >= serv->sv_nrpools)
+		if (++pidx >= nrpools)
 			pidx = 0;
 	}
 
@@ -414,15 +435,13 @@ __svc_create(struct svc_program *prog, int nprogs, struct svc_stat *stats,
 
 	__svc_init_bc(serv);
 
-	serv->sv_nrpools = npools;
-	serv->sv_pools =
-		kzalloc_objs(struct svc_pool, serv->sv_nrpools);
+	serv->sv_pools = kzalloc_objs(struct svc_pool, npools);
 	if (!serv->sv_pools) {
 		kfree(serv);
 		return NULL;
 	}
 
-	for (i = 0; i < serv->sv_nrpools; i++) {
+	for (i = 0; i < npools; i++) {
 		struct svc_pool *pool = &serv->sv_pools[i];
 
 		dprintk("svc: initialising pool %u for %s\n",
@@ -520,7 +539,7 @@ svc_destroy(struct svc_serv **servp)
 
 	cache_clean_deferred(serv);
 
-	for (i = 0; i < serv->sv_nrpools; i++) {
+	for (i = 0; i < svc_serv_nrpools(serv); i++) {
 		struct svc_pool *pool = &serv->sv_pools[i];
 
 		svc_pool_destroy_counters(pool);
@@ -732,7 +751,7 @@ int svc_new_thread(struct svc_serv *serv, struct svc_pool *pool)
 	}
 
 	rqstp->rq_task = task;
-	if (serv->sv_nrpools > 1)
+	if (svc_serv_nrpools(serv) > 1)
 		svc_pool_map_set_cpumask(task, pool->sp_id);
 
 	svc_sock_update_bufs(serv);
@@ -858,8 +877,9 @@ int
 svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
 		    unsigned int nrservs)
 {
-	unsigned int base = nrservs / serv->sv_nrpools;
-	unsigned int remain = nrservs % serv->sv_nrpools;
+	unsigned int nrpools = svc_serv_nrpools(serv);
+	unsigned int base = nrservs / nrpools;
+	unsigned int remain = nrservs % nrpools;
 	int i, err = 0;
 
 	/*
@@ -870,9 +890,9 @@ svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
 	 * @nrservs.
 	 */
 	if (base == 0 && nrservs != 0)
-		remain = serv->sv_nrpools;
+		remain = nrpools;
 
-	for (i = 0; i < serv->sv_nrpools; ++i) {
+	for (i = 0; i < nrpools; ++i) {
 		struct svc_pool *pool = &serv->sv_pools[i];
 		int threads = base;
 
@@ -906,7 +926,7 @@ unsigned int svc_serv_maxthreads(const struct svc_serv *serv)
 {
 	unsigned int i, max = 0;
 
-	for (i = 0; i < serv->sv_nrpools; i++)
+	for (i = 0; i < svc_serv_nrpools(serv); i++)
 		max += data_race(serv->sv_pools[i].sp_nrthrmax);
 	return max;
 }
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 63d1002e63e7..40040af588fb 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -1188,7 +1188,7 @@ static void svc_clean_up_xprts(struct svc_serv *serv, struct net *net)
 	struct svc_xprt *xprt;
 	int i;
 
-	for (i = 0; i < serv->sv_nrpools; i++) {
+	for (i = 0; i < svc_serv_nrpools(serv); i++) {
 		struct svc_pool *pool = &serv->sv_pools[i];
 		struct llist_node *q, **t1, *t2;
 
@@ -1517,7 +1517,7 @@ static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
 		return SEQ_START_TOKEN;
 	if (!si->serv)
 		return NULL;
-	return pidx > si->serv->sv_nrpools ? NULL
+	return pidx > svc_serv_nrpools(si->serv) ? NULL
 		: &si->serv->sv_pools[pidx - 1];
 }
 
@@ -1535,7 +1535,7 @@ static void *svc_pool_stats_next(struct seq_file *m, void *p, loff_t *pos)
 		pool = &serv->sv_pools[0];
 	} else {
 		unsigned int pidx = (pool - &serv->sv_pools[0]);
-		if (pidx < serv->sv_nrpools-1)
+		if (pidx < svc_serv_nrpools(serv) - 1)
 			pool = &serv->sv_pools[pidx+1];
 		else
 			pool = NULL;

-- 
2.55.0

Re: [PATCH v5 5/5] sunrpc: derive the pool count instead of caching it in sv_nrpools

[NeilBrown]

On Mon, 06 Jul 2026, Jeff Layton wrote:
> Now that the pool mode is always pernode, svc_serv.sv_nrpools is
> redundant with sv_is_pooled: an unpooled service always has a single
> pool, and a pooled service has svc_pool_map.npools pools (which is one on
> a single-node host). sv_nrpools cannot distinguish an unpooled service
> from a pooled service that happens to have one pool, so it is sv_nrpools,
> not sv_is_pooled, that carries no unique information.
> 
> Replace the cached field with a svc_serv_nrpools() helper that derives
> the count from sv_is_pooled and the pool map, and convert all readers to
> it. svc_pool_map is file-local to svc.c, so export the helper for the
> svc_xprt.c and nfsd callers.
> 
> Reading svc_pool_map.npools without svc_pool_map_mutex is safe: the
> mutex protects only svc_pool_map.count, and npools is already read
> locklessly in svc_pool_for_cpu().
> 
> A pooled service holds a map reference for its whole lifetime, so npools
> is stable while any reader could observe it.  The hot path
> (svc_pool_for_cpu()) already dereferences svc_pool_map for to_pool, and
> npools shares that cacheline, so there is no new locking or coherence
> cost.
> 
> __svc_create() keeps using its local npools argument for the sv_pools[]
> allocation, since sv_is_pooled is not set until svc_create_pooled() has
> returned from it.
> 
> Doing this also removes a modulus operation from svc_pool_for_cpu(),
> which should make for more efficient RPC queueing.
> 
> Assisted-by: Claude:claude-opus-4-8
> Suggested-by: NeilBrown <neilb@ownmail.net>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/nfsd/nfsctl.c           |  2 +-
>  fs/nfsd/nfssvc.c           | 10 ++++-----
>  include/linux/sunrpc/svc.h |  2 +-
>  net/sunrpc/svc.c           | 52 ++++++++++++++++++++++++++++++++--------------
>  net/sunrpc/svc_xprt.c      |  6 +++---
>  5 files changed, 46 insertions(+), 26 deletions(-)
> 
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index bc16fc7ca24f..0543e5bb842f 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -1526,7 +1526,7 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
>  
>  	rcu_read_lock();
>  
> -	for (i = 0; i < nn->nfsd_serv->sv_nrpools; i++) {
> +	for (i = 0; i < svc_serv_nrpools(nn->nfsd_serv); i++) {
>  		struct svc_rqst *rqstp;
>  		long thread_skip = 0;
>  
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index a8ea4dbfa56b..2edf716ea022 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -655,7 +655,7 @@ int nfsd_nrpools(struct net *net)
>  	if (nn->nfsd_serv == NULL)
>  		return 0;
>  	else
> -		return nn->nfsd_serv->sv_nrpools;
> +		return svc_serv_nrpools(nn->nfsd_serv);
>  }
>  
>  int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
> @@ -665,7 +665,7 @@ int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
>  	int i;
>  
>  	if (serv)
> -		for (i = 0; i < serv->sv_nrpools && i < n; i++)
> +		for (i = 0; i < svc_serv_nrpools(serv) && i < n; i++)
>  			nthreads[i] = serv->sv_pools[i].sp_nrthrmax;
>  	return 0;
>  }
> @@ -699,8 +699,8 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
>  	if (n == 1)
>  		return svc_set_num_threads(nn->nfsd_serv, nn->min_threads, nthreads[0]);
>  
> -	if (n > nn->nfsd_serv->sv_nrpools)
> -		n = nn->nfsd_serv->sv_nrpools;
> +	if (n > svc_serv_nrpools(nn->nfsd_serv))
> +		n = svc_serv_nrpools(nn->nfsd_serv);
>  
>  	/* enforce a global maximum number of threads */
>  	tot = 0;
> @@ -731,7 +731,7 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
>  	}
>  
>  	/* Anything undefined in array is considered to be 0 */
> -	for (i = n; i < nn->nfsd_serv->sv_nrpools; ++i) {
> +	for (i = n; i < svc_serv_nrpools(nn->nfsd_serv); ++i) {
>  		err = svc_set_pool_threads(nn->nfsd_serv,
>  					   &nn->nfsd_serv->sv_pools[i],
>  					   0, 0);
> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> index 3a0152d926fb..3c885ab6ad41 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -85,7 +85,6 @@ struct svc_serv {
>  
>  	char *			sv_name;	/* service name */
>  
> -	unsigned int		sv_nrpools;	/* number of thread pools */
>  	bool			sv_is_pooled;	/* is this a pooled service? */
>  	struct svc_pool *	sv_pools;	/* array of thread pools */
>  	int			(*sv_threadfn)(void *data);
> @@ -480,6 +479,7 @@ void		   svc_wake_up(struct svc_serv *);
>  void		   svc_reserve(struct svc_rqst *rqstp, int space);
>  void		   svc_pool_wake_idle_thread(struct svc_pool *pool);
>  struct svc_pool   *svc_pool_for_cpu(struct svc_serv *serv);
> +unsigned int	   svc_serv_nrpools(const struct svc_serv *serv);
>  char *		   svc_print_addr(struct svc_rqst *, char *, size_t);
>  const char *	   svc_proc_name(const struct svc_rqst *rqstp);
>  int		   svc_encode_result_payload(struct svc_rqst *rqstp,
> diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> index ece69cb0138a..800514a14f17 100644
> --- a/net/sunrpc/svc.c
> +++ b/net/sunrpc/svc.c
> @@ -224,7 +224,7 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
>  	unsigned int node = m->pool_to[pidx];
>  
>  	/*
> -	 * The caller checks for sv_nrpools > 1, which
> +	 * The caller checks for more than one pool, which
>  	 * implies that we've been initialized.
>  	 */
>  	WARN_ON_ONCE(m->count == 0);
> @@ -234,6 +234,24 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
>  	set_cpus_allowed_ptr(task, cpumask_of_node(node));
>  }
>  
> +/**
> + * svc_serv_nrpools - number of thread pools backing a service
> + * @serv: An RPC service
> + *
> + * Pooled services all share the global svc_pool_map, so their pool count
> + * is svc_pool_map.npools. Unpooled services have a single pool. Reading
> + * npools without svc_pool_map_mutex is safe: a pooled service holds a map
> + * reference for its whole lifetime, so npools is stable once set.
> + *
> + * Return value:
> + *   The number of pools in @serv
> + */
> +unsigned int svc_serv_nrpools(const struct svc_serv *serv)
> +{
> +	return serv->sv_is_pooled ? svc_pool_map.npools : 1;
> +}
> +EXPORT_SYMBOL_GPL(svc_serv_nrpools);

I would make this a static-inline.

> +
>  /**
>   * svc_pool_for_cpu - Select pool to run a thread on this cpu
>   * @serv: An RPC service
> @@ -247,12 +265,15 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
>  struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
>  {
>  	struct svc_pool_map *m = &svc_pool_map;
> +	unsigned int nrpools = svc_serv_nrpools(serv);
>  	unsigned int pidx, i;
>  
> -	if (serv->sv_nrpools <= 1)
> +	if (nrpools <= 1)
>  		return serv->sv_pools;
>  
> -	pidx = m->to_pool[cpu_to_node(raw_smp_processor_id())] % serv->sv_nrpools;
> +	pidx = m->to_pool[cpu_to_node(raw_smp_processor_id())];
> +	if (pidx >= nrpools)
> +		pidx = 0;

The values stored in svc_pool_map.to_pool are all less than
svc_pool_map.npools.
So that if() condition cannot be true. 

But those two things don't reduce the correctness of the patch.

Reviewed-by: NeilBrown <neil@brown.name>

Thanks for doing this.
NeilBrown


>  
>  	/*
>  	 * It's possible to have a pool with no threads. Userland can just set
> @@ -265,7 +286,7 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
>  	 * populated pool, trading NUMA locality for a guarantee that the
>  	 * transport is serviced.
>  	 */
> -	for (i = 0; i < serv->sv_nrpools; i++) {
> +	for (i = 0; i < nrpools; i++) {
>  		struct svc_pool *pool = &serv->sv_pools[pidx];
>  
>  		/* This is set under the sp_mutex and rarely ever changes. A
> @@ -274,7 +295,7 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
>  		if (data_race(pool->sp_nrthreads))
>  			return pool;
>  
> -		if (++pidx >= serv->sv_nrpools)
> +		if (++pidx >= nrpools)
>  			pidx = 0;
>  	}
>  
> @@ -414,15 +435,13 @@ __svc_create(struct svc_program *prog, int nprogs, struct svc_stat *stats,
>  
>  	__svc_init_bc(serv);
>  
> -	serv->sv_nrpools = npools;
> -	serv->sv_pools =
> -		kzalloc_objs(struct svc_pool, serv->sv_nrpools);
> +	serv->sv_pools = kzalloc_objs(struct svc_pool, npools);
>  	if (!serv->sv_pools) {
>  		kfree(serv);
>  		return NULL;
>  	}
>  
> -	for (i = 0; i < serv->sv_nrpools; i++) {
> +	for (i = 0; i < npools; i++) {
>  		struct svc_pool *pool = &serv->sv_pools[i];
>  
>  		dprintk("svc: initialising pool %u for %s\n",
> @@ -520,7 +539,7 @@ svc_destroy(struct svc_serv **servp)
>  
>  	cache_clean_deferred(serv);
>  
> -	for (i = 0; i < serv->sv_nrpools; i++) {
> +	for (i = 0; i < svc_serv_nrpools(serv); i++) {
>  		struct svc_pool *pool = &serv->sv_pools[i];
>  
>  		svc_pool_destroy_counters(pool);
> @@ -732,7 +751,7 @@ int svc_new_thread(struct svc_serv *serv, struct svc_pool *pool)
>  	}
>  
>  	rqstp->rq_task = task;
> -	if (serv->sv_nrpools > 1)
> +	if (svc_serv_nrpools(serv) > 1)
>  		svc_pool_map_set_cpumask(task, pool->sp_id);
>  
>  	svc_sock_update_bufs(serv);
> @@ -858,8 +877,9 @@ int
>  svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
>  		    unsigned int nrservs)
>  {
> -	unsigned int base = nrservs / serv->sv_nrpools;
> -	unsigned int remain = nrservs % serv->sv_nrpools;
> +	unsigned int nrpools = svc_serv_nrpools(serv);
> +	unsigned int base = nrservs / nrpools;
> +	unsigned int remain = nrservs % nrpools;
>  	int i, err = 0;
>  
>  	/*
> @@ -870,9 +890,9 @@ svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
>  	 * @nrservs.
>  	 */
>  	if (base == 0 && nrservs != 0)
> -		remain = serv->sv_nrpools;
> +		remain = nrpools;
>  
> -	for (i = 0; i < serv->sv_nrpools; ++i) {
> +	for (i = 0; i < nrpools; ++i) {
>  		struct svc_pool *pool = &serv->sv_pools[i];
>  		int threads = base;
>  
> @@ -906,7 +926,7 @@ unsigned int svc_serv_maxthreads(const struct svc_serv *serv)
>  {
>  	unsigned int i, max = 0;
>  
> -	for (i = 0; i < serv->sv_nrpools; i++)
> +	for (i = 0; i < svc_serv_nrpools(serv); i++)
>  		max += data_race(serv->sv_pools[i].sp_nrthrmax);
>  	return max;
>  }
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index 63d1002e63e7..40040af588fb 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -1188,7 +1188,7 @@ static void svc_clean_up_xprts(struct svc_serv *serv, struct net *net)
>  	struct svc_xprt *xprt;
>  	int i;
>  
> -	for (i = 0; i < serv->sv_nrpools; i++) {
> +	for (i = 0; i < svc_serv_nrpools(serv); i++) {
>  		struct svc_pool *pool = &serv->sv_pools[i];
>  		struct llist_node *q, **t1, *t2;
>  
> @@ -1517,7 +1517,7 @@ static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
>  		return SEQ_START_TOKEN;
>  	if (!si->serv)
>  		return NULL;
> -	return pidx > si->serv->sv_nrpools ? NULL
> +	return pidx > svc_serv_nrpools(si->serv) ? NULL
>  		: &si->serv->sv_pools[pidx - 1];
>  }
>  
> @@ -1535,7 +1535,7 @@ static void *svc_pool_stats_next(struct seq_file *m, void *p, loff_t *pos)
>  		pool = &serv->sv_pools[0];
>  	} else {
>  		unsigned int pidx = (pool - &serv->sv_pools[0]);
> -		if (pidx < serv->sv_nrpools-1)
> +		if (pidx < svc_serv_nrpools(serv) - 1)
>  			pool = &serv->sv_pools[pidx+1];
>  		else
>  			pool = NULL;
> 
> -- 
> 2.55.0
> 
> 

Re: [PATCH v5 5/5] sunrpc: derive the pool count instead of caching it in sv_nrpools

[Jeff Layton]

On Tue, 2026-07-07 at 08:50 +1000, NeilBrown wrote:
> On Mon, 06 Jul 2026, Jeff Layton wrote:
> > Now that the pool mode is always pernode, svc_serv.sv_nrpools is
> > redundant with sv_is_pooled: an unpooled service always has a single
> > pool, and a pooled service has svc_pool_map.npools pools (which is one on
> > a single-node host). sv_nrpools cannot distinguish an unpooled service
> > from a pooled service that happens to have one pool, so it is sv_nrpools,
> > not sv_is_pooled, that carries no unique information.
> > 
> > Replace the cached field with a svc_serv_nrpools() helper that derives
> > the count from sv_is_pooled and the pool map, and convert all readers to
> > it. svc_pool_map is file-local to svc.c, so export the helper for the
> > svc_xprt.c and nfsd callers.
> > 
> > Reading svc_pool_map.npools without svc_pool_map_mutex is safe: the
> > mutex protects only svc_pool_map.count, and npools is already read
> > locklessly in svc_pool_for_cpu().
> > 
> > A pooled service holds a map reference for its whole lifetime, so npools
> > is stable while any reader could observe it.  The hot path
> > (svc_pool_for_cpu()) already dereferences svc_pool_map for to_pool, and
> > npools shares that cacheline, so there is no new locking or coherence
> > cost.
> > 
> > __svc_create() keeps using its local npools argument for the sv_pools[]
> > allocation, since sv_is_pooled is not set until svc_create_pooled() has
> > returned from it.
> > 
> > Doing this also removes a modulus operation from svc_pool_for_cpu(),
> > which should make for more efficient RPC queueing.
> > 
> > Assisted-by: Claude:claude-opus-4-8
> > Suggested-by: NeilBrown <neilb@ownmail.net>
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >  fs/nfsd/nfsctl.c           |  2 +-
> >  fs/nfsd/nfssvc.c           | 10 ++++-----
> >  include/linux/sunrpc/svc.h |  2 +-
> >  net/sunrpc/svc.c           | 52 ++++++++++++++++++++++++++++++++--------------
> >  net/sunrpc/svc_xprt.c      |  6 +++---
> >  5 files changed, 46 insertions(+), 26 deletions(-)
> > 
> > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> > index bc16fc7ca24f..0543e5bb842f 100644
> > --- a/fs/nfsd/nfsctl.c
> > +++ b/fs/nfsd/nfsctl.c
> > @@ -1526,7 +1526,7 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
> >  
> >  	rcu_read_lock();
> >  
> > -	for (i = 0; i < nn->nfsd_serv->sv_nrpools; i++) {
> > +	for (i = 0; i < svc_serv_nrpools(nn->nfsd_serv); i++) {
> >  		struct svc_rqst *rqstp;
> >  		long thread_skip = 0;
> >  
> > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> > index a8ea4dbfa56b..2edf716ea022 100644
> > --- a/fs/nfsd/nfssvc.c
> > +++ b/fs/nfsd/nfssvc.c
> > @@ -655,7 +655,7 @@ int nfsd_nrpools(struct net *net)
> >  	if (nn->nfsd_serv == NULL)
> >  		return 0;
> >  	else
> > -		return nn->nfsd_serv->sv_nrpools;
> > +		return svc_serv_nrpools(nn->nfsd_serv);
> >  }
> >  
> >  int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
> > @@ -665,7 +665,7 @@ int nfsd_get_nrthreads(int n, int *nthreads, struct net *net)
> >  	int i;
> >  
> >  	if (serv)
> > -		for (i = 0; i < serv->sv_nrpools && i < n; i++)
> > +		for (i = 0; i < svc_serv_nrpools(serv) && i < n; i++)
> >  			nthreads[i] = serv->sv_pools[i].sp_nrthrmax;
> >  	return 0;
> >  }
> > @@ -699,8 +699,8 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
> >  	if (n == 1)
> >  		return svc_set_num_threads(nn->nfsd_serv, nn->min_threads, nthreads[0]);
> >  
> > -	if (n > nn->nfsd_serv->sv_nrpools)
> > -		n = nn->nfsd_serv->sv_nrpools;
> > +	if (n > svc_serv_nrpools(nn->nfsd_serv))
> > +		n = svc_serv_nrpools(nn->nfsd_serv);
> >  
> >  	/* enforce a global maximum number of threads */
> >  	tot = 0;
> > @@ -731,7 +731,7 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
> >  	}
> >  
> >  	/* Anything undefined in array is considered to be 0 */
> > -	for (i = n; i < nn->nfsd_serv->sv_nrpools; ++i) {
> > +	for (i = n; i < svc_serv_nrpools(nn->nfsd_serv); ++i) {
> >  		err = svc_set_pool_threads(nn->nfsd_serv,
> >  					   &nn->nfsd_serv->sv_pools[i],
> >  					   0, 0);
> > diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> > index 3a0152d926fb..3c885ab6ad41 100644
> > --- a/include/linux/sunrpc/svc.h
> > +++ b/include/linux/sunrpc/svc.h
> > @@ -85,7 +85,6 @@ struct svc_serv {
> >  
> >  	char *			sv_name;	/* service name */
> >  
> > -	unsigned int		sv_nrpools;	/* number of thread pools */
> >  	bool			sv_is_pooled;	/* is this a pooled service? */
> >  	struct svc_pool *	sv_pools;	/* array of thread pools */
> >  	int			(*sv_threadfn)(void *data);
> > @@ -480,6 +479,7 @@ void		   svc_wake_up(struct svc_serv *);
> >  void		   svc_reserve(struct svc_rqst *rqstp, int space);
> >  void		   svc_pool_wake_idle_thread(struct svc_pool *pool);
> >  struct svc_pool   *svc_pool_for_cpu(struct svc_serv *serv);
> > +unsigned int	   svc_serv_nrpools(const struct svc_serv *serv);
> >  char *		   svc_print_addr(struct svc_rqst *, char *, size_t);
> >  const char *	   svc_proc_name(const struct svc_rqst *rqstp);
> >  int		   svc_encode_result_payload(struct svc_rqst *rqstp,
> > diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
> > index ece69cb0138a..800514a14f17 100644
> > --- a/net/sunrpc/svc.c
> > +++ b/net/sunrpc/svc.c
> > @@ -224,7 +224,7 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
> >  	unsigned int node = m->pool_to[pidx];
> >  
> >  	/*
> > -	 * The caller checks for sv_nrpools > 1, which
> > +	 * The caller checks for more than one pool, which
> >  	 * implies that we've been initialized.
> >  	 */
> >  	WARN_ON_ONCE(m->count == 0);
> > @@ -234,6 +234,24 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
> >  	set_cpus_allowed_ptr(task, cpumask_of_node(node));
> >  }
> >  
> > +/**
> > + * svc_serv_nrpools - number of thread pools backing a service
> > + * @serv: An RPC service
> > + *
> > + * Pooled services all share the global svc_pool_map, so their pool count
> > + * is svc_pool_map.npools. Unpooled services have a single pool. Reading
> > + * npools without svc_pool_map_mutex is safe: a pooled service holds a map
> > + * reference for its whole lifetime, so npools is stable once set.
> > + *
> > + * Return value:
> > + *   The number of pools in @serv
> > + */
> > +unsigned int svc_serv_nrpools(const struct svc_serv *serv)
> > +{
> > +	return serv->sv_is_pooled ? svc_pool_map.npools : 1;
> > +}
> > +EXPORT_SYMBOL_GPL(svc_serv_nrpools);
> 
> I would make this a static-inline.
> 

That would mean that we would have to export svc_pool_map, which is
currently private to svc.c.

> > +
> >  /**
> >   * svc_pool_for_cpu - Select pool to run a thread on this cpu
> >   * @serv: An RPC service
> > @@ -247,12 +265,15 @@ svc_pool_map_set_cpumask(struct task_struct *task, unsigned int pidx)
> >  struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
> >  {
> >  	struct svc_pool_map *m = &svc_pool_map;
> > +	unsigned int nrpools = svc_serv_nrpools(serv);
> >  	unsigned int pidx, i;
> >  
> > -	if (serv->sv_nrpools <= 1)
> > +	if (nrpools <= 1)
> >  		return serv->sv_pools;
> >  
> > -	pidx = m->to_pool[cpu_to_node(raw_smp_processor_id())] % serv->sv_nrpools;
> > +	pidx = m->to_pool[cpu_to_node(raw_smp_processor_id())];
> > +	if (pidx >= nrpools)
> > +		pidx = 0;
> 
> The values stored in svc_pool_map.to_pool are all less than
> svc_pool_map.npools.
> So that if() condition cannot be true. 
> 
> But those two things don't reduce the correctness of the patch.
> 
> Reviewed-by: NeilBrown <neil@brown.name>
> 
> Thanks for doing this.
> NeilBrown
> 

Ahh good point. I guess we can remove that if statement. I can send
Chuck a follow-on patch. Thanks for the R-b!

> 
> >  
> >  	/*
> >  	 * It's possible to have a pool with no threads. Userland can just set
> > @@ -265,7 +286,7 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
> >  	 * populated pool, trading NUMA locality for a guarantee that the
> >  	 * transport is serviced.
> >  	 */
> > -	for (i = 0; i < serv->sv_nrpools; i++) {
> > +	for (i = 0; i < nrpools; i++) {
> >  		struct svc_pool *pool = &serv->sv_pools[pidx];
> >  
> >  		/* This is set under the sp_mutex and rarely ever changes. A
> > @@ -274,7 +295,7 @@ struct svc_pool *svc_pool_for_cpu(struct svc_serv *serv)
> >  		if (data_race(pool->sp_nrthreads))
> >  			return pool;
> >  
> > -		if (++pidx >= serv->sv_nrpools)
> > +		if (++pidx >= nrpools)
> >  			pidx = 0;
> >  	}
> >  
> > @@ -414,15 +435,13 @@ __svc_create(struct svc_program *prog, int nprogs, struct svc_stat *stats,
> >  
> >  	__svc_init_bc(serv);
> >  
> > -	serv->sv_nrpools = npools;
> > -	serv->sv_pools =
> > -		kzalloc_objs(struct svc_pool, serv->sv_nrpools);
> > +	serv->sv_pools = kzalloc_objs(struct svc_pool, npools);
> >  	if (!serv->sv_pools) {
> >  		kfree(serv);
> >  		return NULL;
> >  	}
> >  
> > -	for (i = 0; i < serv->sv_nrpools; i++) {
> > +	for (i = 0; i < npools; i++) {
> >  		struct svc_pool *pool = &serv->sv_pools[i];
> >  
> >  		dprintk("svc: initialising pool %u for %s\n",
> > @@ -520,7 +539,7 @@ svc_destroy(struct svc_serv **servp)
> >  
> >  	cache_clean_deferred(serv);
> >  
> > -	for (i = 0; i < serv->sv_nrpools; i++) {
> > +	for (i = 0; i < svc_serv_nrpools(serv); i++) {
> >  		struct svc_pool *pool = &serv->sv_pools[i];
> >  
> >  		svc_pool_destroy_counters(pool);
> > @@ -732,7 +751,7 @@ int svc_new_thread(struct svc_serv *serv, struct svc_pool *pool)
> >  	}
> >  
> >  	rqstp->rq_task = task;
> > -	if (serv->sv_nrpools > 1)
> > +	if (svc_serv_nrpools(serv) > 1)
> >  		svc_pool_map_set_cpumask(task, pool->sp_id);
> >  
> >  	svc_sock_update_bufs(serv);
> > @@ -858,8 +877,9 @@ int
> >  svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
> >  		    unsigned int nrservs)
> >  {
> > -	unsigned int base = nrservs / serv->sv_nrpools;
> > -	unsigned int remain = nrservs % serv->sv_nrpools;
> > +	unsigned int nrpools = svc_serv_nrpools(serv);
> > +	unsigned int base = nrservs / nrpools;
> > +	unsigned int remain = nrservs % nrpools;
> >  	int i, err = 0;
> >  
> >  	/*
> > @@ -870,9 +890,9 @@ svc_set_num_threads(struct svc_serv *serv, unsigned int min_threads,
> >  	 * @nrservs.
> >  	 */
> >  	if (base == 0 && nrservs != 0)
> > -		remain = serv->sv_nrpools;
> > +		remain = nrpools;
> >  
> > -	for (i = 0; i < serv->sv_nrpools; ++i) {
> > +	for (i = 0; i < nrpools; ++i) {
> >  		struct svc_pool *pool = &serv->sv_pools[i];
> >  		int threads = base;
> >  
> > @@ -906,7 +926,7 @@ unsigned int svc_serv_maxthreads(const struct svc_serv *serv)
> >  {
> >  	unsigned int i, max = 0;
> >  
> > -	for (i = 0; i < serv->sv_nrpools; i++)
> > +	for (i = 0; i < svc_serv_nrpools(serv); i++)
> >  		max += data_race(serv->sv_pools[i].sp_nrthrmax);
> >  	return max;
> >  }
> > diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> > index 63d1002e63e7..40040af588fb 100644
> > --- a/net/sunrpc/svc_xprt.c
> > +++ b/net/sunrpc/svc_xprt.c
> > @@ -1188,7 +1188,7 @@ static void svc_clean_up_xprts(struct svc_serv *serv, struct net *net)
> >  	struct svc_xprt *xprt;
> >  	int i;
> >  
> > -	for (i = 0; i < serv->sv_nrpools; i++) {
> > +	for (i = 0; i < svc_serv_nrpools(serv); i++) {
> >  		struct svc_pool *pool = &serv->sv_pools[i];
> >  		struct llist_node *q, **t1, *t2;
> >  
> > @@ -1517,7 +1517,7 @@ static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
> >  		return SEQ_START_TOKEN;
> >  	if (!si->serv)
> >  		return NULL;
> > -	return pidx > si->serv->sv_nrpools ? NULL
> > +	return pidx > svc_serv_nrpools(si->serv) ? NULL
> >  		: &si->serv->sv_pools[pidx - 1];
> >  }
> >  
> > @@ -1535,7 +1535,7 @@ static void *svc_pool_stats_next(struct seq_file *m, void *p, loff_t *pos)
> >  		pool = &serv->sv_pools[0];
> >  	} else {
> >  		unsigned int pidx = (pool - &serv->sv_pools[0]);
> > -		if (pidx < serv->sv_nrpools-1)
> > +		if (pidx < svc_serv_nrpools(serv) - 1)
> >  			pool = &serv->sv_pools[pidx+1];
> >  		else
> >  			pool = NULL;
> > 
> > -- 
> > 2.55.0
> > 
> > 

-- 
Jeff Layton <jlayton@kernel.org>

Re: [PATCH v5 0/5] sunrpc: hardcode pool_mode to pernode, remove other modes

[Chuck Lever]

On Mon, 06 Jul 2026 09:29:20 -0400, Jeff Layton wrote:
> This has a few small fixes and comment cleanups and also implements
> Neil's suggestion to remove serv.sv_nrpools:
> 
> Patches #1 and #3 address what is a shortcoming of the existing code --
> namely that the server can be configured to schedule RPCs to pools with
> no threads in them.
> 
> [...]

Applied to nfsd-testing, thanks!

[1/5] sunrpc: route to a populated pool in svc_pool_for_cpu()
      commit: abf002b5412b282ce825cf0ada22f0278ae7f408
[2/5] sunrpc: hardcode pool_mode to pernode, remove other modes
      commit: cb4ab2c71e09f8c958ecc7bf07270ae78584f85a
[3/5] sunrpc: guarantee a thread per pool when auto-distributing
      commit: c972bef38717f27c282592bca22890f49233ec0a
[4/5] sunrpc: tear down pool counters before dropping the pool map reference
      commit: 9b6f69571d09627b8b4303be0f257c0e36d9d3fd
[5/5] sunrpc: derive the pool count instead of caching it in sv_nrpools
      commit: 9435623ac560654825a62ee4b628ae4bbaa87920

--
Chuck Lever