[PATCH RFC 4/6] sunrpc: introduce the concept of a minimum number of threads per pool

[Jeff Layton <jlayton@kernel.org>]

Add a new pool->sp_nrthrmin field to track the minimum number of threads
in a pool. Add min_threads parameters to both svc_set_num_threads() and
svc_set_pool_threads(). If min_threads is non-zero, then have
svc_set_num_threads() ensure that the number of running threads is
between the min and the max.

For now, the min_threads is always 0, but a later patch will pass the
proper value through from nfsd.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/lockd/svc.c             |  4 ++--
 fs/nfs/callback.c          |  8 ++++----
 fs/nfsd/nfssvc.c           |  8 ++++----
 include/linux/sunrpc/svc.h |  7 ++++---
 net/sunrpc/svc.c           | 21 ++++++++++++++++++---
 5 files changed, 32 insertions(+), 16 deletions(-)

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index fbf132b4e08d11a91784c21ee0209fd7c149fd9d..7899205314391415dfb698ab58fe97efc426d928 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -340,7 +340,7 @@ static int lockd_get(void)
 		return -ENOMEM;
 	}
 
-	error = svc_set_num_threads(serv, 1);
+	error = svc_set_num_threads(serv, 1, 0);
 	if (error < 0) {
 		svc_destroy(&serv);
 		return error;
@@ -368,7 +368,7 @@ static void lockd_put(void)
 	unregister_inet6addr_notifier(&lockd_inet6addr_notifier);
 #endif
 
-	svc_set_num_threads(nlmsvc_serv, 0);
+	svc_set_num_threads(nlmsvc_serv, 0, 0);
 	timer_delete_sync(&nlmsvc_retry);
 	svc_destroy(&nlmsvc_serv);
 	dprintk("lockd_down: service destroyed\n");
diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 44b35b7f8dc022f1d8c069eaf2f7d334c93f77fc..32bbc0e688ff3988e4ba50eeb36b4808cec07c87 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -119,9 +119,9 @@ static int nfs_callback_start_svc(int minorversion, struct rpc_xprt *xprt,
 	if (serv->sv_nrthreads == nrservs)
 		return 0;
 
-	ret = svc_set_num_threads(serv, nrservs);
+	ret = svc_set_num_threads(serv, nrservs, 0);
 	if (ret) {
-		svc_set_num_threads(serv, 0);
+		svc_set_num_threads(serv, 0, 0);
 		return ret;
 	}
 	dprintk("nfs_callback_up: service started\n");
@@ -242,7 +242,7 @@ int nfs_callback_up(u32 minorversion, struct rpc_xprt *xprt)
 	cb_info->users++;
 err_net:
 	if (!cb_info->users) {
-		svc_set_num_threads(cb_info->serv, 0);
+		svc_set_num_threads(cb_info->serv, 0, 0);
 		svc_destroy(&cb_info->serv);
 	}
 err_create:
@@ -268,7 +268,7 @@ void nfs_callback_down(int minorversion, struct net *net)
 	nfs_callback_down_net(minorversion, serv, net);
 	cb_info->users--;
 	if (cb_info->users == 0) {
-		svc_set_num_threads(serv, 0);
+		svc_set_num_threads(serv, 0, 0);
 		dprintk("nfs_callback_down: service destroyed\n");
 		svc_destroy(&cb_info->serv);
 	}
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index aafec8ff588b85b0e26d40b76ef00953dc6472b4..993ed338764b0ccd7bdfb76bd6fbb5dc6ab4022d 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -594,7 +594,7 @@ void nfsd_shutdown_threads(struct net *net)
 	}
 
 	/* Kill outstanding nfsd threads */
-	svc_set_num_threads(serv, 0);
+	svc_set_num_threads(serv, 0, 0);
 	nfsd_destroy_serv(net);
 	mutex_unlock(&nfsd_mutex);
 }
@@ -704,7 +704,7 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 
 	/* Special case: When n == 1, distribute threads equally among pools. */
 	if (n == 1)
-		return svc_set_num_threads(nn->nfsd_serv, nthreads[0]);
+		return svc_set_num_threads(nn->nfsd_serv, nthreads[0], 0);
 
 	if (n > nn->nfsd_serv->sv_nrpools)
 		n = nn->nfsd_serv->sv_nrpools;
@@ -732,7 +732,7 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 	for (i = 0; i < n; i++) {
 		err = svc_set_pool_threads(nn->nfsd_serv,
 					   &nn->nfsd_serv->sv_pools[i],
-					   nthreads[i]);
+					   nthreads[i], 0);
 		if (err)
 			goto out;
 	}
@@ -741,7 +741,7 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
 	for (i = n; i < nn->nfsd_serv->sv_nrpools; ++i) {
 		err = svc_set_pool_threads(nn->nfsd_serv,
 					   &nn->nfsd_serv->sv_pools[i],
-					   0);
+					   0, 0);
 		if (err)
 			goto out;
 	}
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index ee9260ca908c907f4373f4cfa471b272bc7bcc8c..35bd3247764ae8dc5dcdfffeea36f7cfefd13372 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -36,6 +36,7 @@
 struct svc_pool {
 	unsigned int		sp_id;		/* pool id; also node id on NUMA */
 	unsigned int		sp_nrthreads;	/* # of threads currently running in pool */
+	unsigned int		sp_nrthrmin;	/* Min number of threads to run per pool */
 	unsigned int		sp_nrthrmax;	/* Max requested number of threads in pool */
 	struct lwq		sp_xprts;	/* pending transports */
 	struct list_head	sp_all_threads;	/* all server threads */
@@ -72,7 +73,7 @@ struct svc_serv {
 	struct svc_stat *	sv_stats;	/* RPC statistics */
 	spinlock_t		sv_lock;
 	unsigned int		sv_nprogs;	/* Number of sv_programs */
-	unsigned int		sv_nrthreads;	/* # of server threads */
+	unsigned int		sv_nrthreads;	/* # of running server threads */
 	unsigned int		sv_max_payload;	/* datagram payload size */
 	unsigned int		sv_max_mesg;	/* max_payload + 1 page for overheads */
 	unsigned int		sv_xdrsize;	/* XDR buffer size */
@@ -447,8 +448,8 @@ struct svc_serv *  svc_create_pooled(struct svc_program *prog,
 				     struct svc_stat *stats,
 				     unsigned int bufsize,
 				     int (*threadfn)(void *data));
-int		   svc_set_pool_threads(struct svc_serv *, struct svc_pool *, int);
-int		   svc_set_num_threads(struct svc_serv *, int);
+int		   svc_set_pool_threads(struct svc_serv *, struct svc_pool *, int, unsigned int);
+int		   svc_set_num_threads(struct svc_serv *, int, unsigned int);
 int		   svc_pool_stats_open(struct svc_info *si, struct file *file);
 void		   svc_process(struct svc_rqst *rqstp);
 void		   svc_process_bc(struct rpc_rqst *req, struct svc_rqst *rqstp);
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 8cd45f62ef74af6e0826b8f13cc903b0962af5e0..dc818158f8529b62dcf96c91bd9a9d4ab21df91f 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -821,6 +821,7 @@ svc_stop_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
  * @serv: RPC service to adjust
  * @pool: Specific pool from which to choose threads
  * @nrservs: New number of threads for @serv (0 or less means kill all threads)
+ * @min_threads: minimum number of threads per pool (0 means set to same as nrservs)
  *
  * Create or destroy threads in @pool to bring it to @nrservs.
  *
@@ -831,12 +832,22 @@ svc_stop_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
  * starting a thread.
  */
 int
-svc_set_pool_threads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
+svc_set_pool_threads(struct svc_serv *serv, struct svc_pool *pool, int nrservs,
+		     unsigned int min_threads)
 {
 	if (!pool)
 		return -EINVAL;
 
 	pool->sp_nrthrmax = nrservs;
+	if (min_threads) {
+		if (pool->sp_nrthreads > nrservs) {
+			// fallthrough to update nrservs
+		} else if (pool->sp_nrthreads < min_threads) {
+			nrservs = min_threads;
+		} else {
+			return 0;
+		}
+	}
 	nrservs -= pool->sp_nrthreads;
 
 	if (nrservs > 0)
@@ -851,6 +862,7 @@ EXPORT_SYMBOL_GPL(svc_set_pool_threads);
  * svc_set_num_threads - adjust number of threads in serv
  * @serv: RPC service to adjust
  * @nrservs: New number of threads for @serv (0 or less means kill all threads)
+ * @min_threads: minimum number of threads per pool (0 means set to same as nrservs)
  *
  * Create or destroy threads in @serv to bring it to @nrservs. If there
  * are multiple pools then the new threads or victims will be distributed
@@ -863,20 +875,23 @@ EXPORT_SYMBOL_GPL(svc_set_pool_threads);
  * starting a thread.
  */
 int
-svc_set_num_threads(struct svc_serv *serv, int nrservs)
+svc_set_num_threads(struct svc_serv *serv, int nrservs, unsigned int min_threads)
 {
 	int base = nrservs / serv->sv_nrpools;
 	int remain = nrservs % serv->sv_nrpools;
 	int i, err;
 
 	for (i = 0; i < serv->sv_nrpools; ++i) {
+		struct svc_pool *pool = &serv->sv_pools[i];
 		int threads = base;
 
 		if (remain) {
 			++threads;
 			--remain;
 		}
-		err = svc_set_pool_threads(serv, &serv->sv_pools[i], threads);
+
+		pool->sp_nrthrmin = min_threads;
+		err = svc_set_pool_threads(serv, pool, threads, min_threads);
 		if (err)
 			break;
 	}

-- 
2.52.0