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Message-Id: <476dcf18-242c-40b2-8afa-ca2128fe4895@app.fastmail.com>
Date: Sat, 13 Dec 2025 16:10:29 -0500
From: "Chuck Lever" <cel@...nel.org>
To: "Jeff Layton" <jlayton@...nel.org>,
"Chuck Lever" <chuck.lever@...cle.com>, NeilBrown <neil@...wn.name>,
"Olga Kornievskaia" <okorniev@...hat.com>, "Dai Ngo" <Dai.Ngo@...cle.com>,
"Tom Talpey" <tom@...pey.com>, "Trond Myklebust" <trondmy@...nel.org>,
"Anna Schumaker" <anna@...nel.org>
Cc: linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 6/6] nfsd: add controls to set the minimum number of threads
per pool
On Fri, Dec 12, 2025, at 5:39 PM, Jeff Layton wrote:
> Add a new "min_threads" variable to the nfsd_net, along with the
> corresponding nfsdfs and netlink interfaces to set that value from
> userland. Pass that value to svc_set_pool_threads() and
> svc_set_num_threads().
>
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
> Documentation/netlink/specs/nfsd.yaml | 5 ++++
> fs/nfsd/netlink.c | 5 ++--
> fs/nfsd/netns.h | 6 +++++
> fs/nfsd/nfsctl.c | 50 +++++++++++++++++++++++++++++++++++
> fs/nfsd/nfssvc.c | 8 +++---
> fs/nfsd/trace.h | 19 +++++++++++++
> include/uapi/linux/nfsd_netlink.h | 1 +
> 7 files changed, 88 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/netlink/specs/nfsd.yaml
> b/Documentation/netlink/specs/nfsd.yaml
> index
> 100363029e82aed87295e34a008ab771a95d508c..badb2fe57c9859c6932c621a589da694782b0272
> 100644
> --- a/Documentation/netlink/specs/nfsd.yaml
> +++ b/Documentation/netlink/specs/nfsd.yaml
> @@ -78,6 +78,9 @@ attribute-sets:
> -
> name: scope
> type: string
> + -
> + name: min-threads
> + type: u32
> -
> name: version
> attributes:
> @@ -159,6 +162,7 @@ operations:
> - gracetime
> - leasetime
> - scope
> + - min-threads
> -
> name: threads-get
> doc: get the number of running threads
> @@ -170,6 +174,7 @@ operations:
> - gracetime
> - leasetime
> - scope
> + - min-threads
> -
> name: version-set
> doc: set nfs enabled versions
> diff --git a/fs/nfsd/netlink.c b/fs/nfsd/netlink.c
> index
> ac51a44e1065ec3f1d88165f70a831a828b58394..887525964451e640304371e33aa4f415b4ff2848
> 100644
> --- a/fs/nfsd/netlink.c
> +++ b/fs/nfsd/netlink.c
> @@ -24,11 +24,12 @@ const struct nla_policy
> nfsd_version_nl_policy[NFSD_A_VERSION_ENABLED + 1] = {
> };
>
> /* NFSD_CMD_THREADS_SET - do */
> -static const struct nla_policy
> nfsd_threads_set_nl_policy[NFSD_A_SERVER_SCOPE + 1] = {
> +static const struct nla_policy
> nfsd_threads_set_nl_policy[NFSD_A_SERVER_MIN_THREADS + 1] = {
> [NFSD_A_SERVER_THREADS] = { .type = NLA_U32, },
> [NFSD_A_SERVER_GRACETIME] = { .type = NLA_U32, },
> [NFSD_A_SERVER_LEASETIME] = { .type = NLA_U32, },
> [NFSD_A_SERVER_SCOPE] = { .type = NLA_NUL_STRING, },
> + [NFSD_A_SERVER_MIN_THREADS] = { .type = NLA_U32, },
> };
>
> /* NFSD_CMD_VERSION_SET - do */
> @@ -57,7 +58,7 @@ static const struct genl_split_ops nfsd_nl_ops[] = {
> .cmd = NFSD_CMD_THREADS_SET,
> .doit = nfsd_nl_threads_set_doit,
> .policy = nfsd_threads_set_nl_policy,
> - .maxattr = NFSD_A_SERVER_SCOPE,
> + .maxattr = NFSD_A_SERVER_MIN_THREADS,
> .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
> },
> {
> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> index
> 3e2d0fde80a7ce434ef2cce9f1666c2bd16ab2eb..1c3449810eaefea8167ddd284af7bd66cac7e211
> 100644
> --- a/fs/nfsd/netns.h
> +++ b/fs/nfsd/netns.h
> @@ -128,6 +128,12 @@ struct nfsd_net {
> seqlock_t writeverf_lock;
> unsigned char writeverf[8];
>
> + /*
> + * Minimum number of threads to run per pool. If 0 then the
> + * min == max requested number of threads.
> + */
> + unsigned int min_threads;
> +
> u32 clientid_base;
> u32 clientid_counter;
> u32 clverifier_counter;
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index
> 206534fccf36a992026669fee6533adff1062c36..a5401015e62499d07150cde8822f1e7dd0515dfe
> 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -48,6 +48,7 @@ enum {
> NFSD_Versions,
> NFSD_Ports,
> NFSD_MaxBlkSize,
> + NFSD_MinThreads,
> NFSD_Filecache,
> NFSD_Leasetime,
> NFSD_Gracetime,
> @@ -67,6 +68,7 @@ static ssize_t write_pool_threads(struct file *file,
> char *buf, size_t size);
> static ssize_t write_versions(struct file *file, char *buf, size_t
> size);
> static ssize_t write_ports(struct file *file, char *buf, size_t size);
> static ssize_t write_maxblksize(struct file *file, char *buf, size_t
> size);
> +static ssize_t write_minthreads(struct file *file, char *buf, size_t
> size);
> #ifdef CONFIG_NFSD_V4
> static ssize_t write_leasetime(struct file *file, char *buf, size_t
> size);
> static ssize_t write_gracetime(struct file *file, char *buf, size_t
> size);
> @@ -85,6 +87,7 @@ static ssize_t (*const write_op[])(struct file *,
> char *, size_t) = {
> [NFSD_Versions] = write_versions,
> [NFSD_Ports] = write_ports,
> [NFSD_MaxBlkSize] = write_maxblksize,
> + [NFSD_MinThreads] = write_minthreads,
> #ifdef CONFIG_NFSD_V4
> [NFSD_Leasetime] = write_leasetime,
> [NFSD_Gracetime] = write_gracetime,
> @@ -899,6 +902,46 @@ static ssize_t write_maxblksize(struct file *file,
> char *buf, size_t size)
> nfsd_max_blksize);
> }
>
> +/*
> + * write_minthreads - Set or report the current min number of threads
> + *
> + * Input:
> + * buf: ignored
> + * size: zero
> + * OR
> + *
> + * Input:
> + * buf: C string containing an unsigned
> + * integer value representing the new
> + * max number of threads
s/max number of threads/min number of threads
> + * size: non-zero length of C string in @buf
> + * Output:
> + * On success: passed-in buffer filled with '\n'-terminated C string
> + * containing numeric value of min_threads setting
> + * for this net namespace;
> + * return code is the size in bytes of the string
> + * On error: return code is zero or a negative errno value
> + */
> +static ssize_t write_minthreads(struct file *file, char *buf, size_t
> size)
> +{
> + char *mesg = buf;
> + struct nfsd_net *nn = net_generic(netns(file), nfsd_net_id);
> + unsigned int minthreads = nn->min_threads;
> +
> + if (size > 0) {
What if @size is a very large number?
> + int rv = get_uint(&mesg, &minthreads);
> +
> + if (rv)
> + return rv;
> + trace_nfsd_ctl_minthreads(netns(file), minthreads);
> + mutex_lock(&nfsd_mutex);
> + nn->min_threads = minthreads;
> + mutex_unlock(&nfsd_mutex);
> + }
> +
> + return scnprintf(buf, SIMPLE_TRANSACTION_LIMIT, "%u\n", minthreads);
> +}
> +
> #ifdef CONFIG_NFSD_V4
> static ssize_t __nfsd4_write_time(struct file *file, char *buf, size_t
> size,
> time64_t *time, struct nfsd_net *nn)
> @@ -1292,6 +1335,7 @@ static int nfsd_fill_super(struct super_block
> *sb, struct fs_context *fc)
> [NFSD_Versions] = {"versions", &transaction_ops, S_IWUSR|S_IRUSR},
> [NFSD_Ports] = {"portlist", &transaction_ops, S_IWUSR|S_IRUGO},
> [NFSD_MaxBlkSize] = {"max_block_size", &transaction_ops,
> S_IWUSR|S_IRUGO},
> + [NFSD_MinThreads] = {"min_threads", &transaction_ops,
> S_IWUSR|S_IRUGO},
> [NFSD_Filecache] = {"filecache", &nfsd_file_cache_stats_fops,
> S_IRUGO},
> #ifdef CONFIG_NFSD_V4
> [NFSD_Leasetime] = {"nfsv4leasetime", &transaction_ops,
> S_IWUSR|S_IRUSR},
> @@ -1636,6 +1680,10 @@ int nfsd_nl_threads_set_doit(struct sk_buff
> *skb, struct genl_info *info)
> scope = nla_data(attr);
> }
>
> + attr = info->attrs[NFSD_A_SERVER_MIN_THREADS];
> + if (attr)
> + nn->min_threads = nla_get_u32(attr);
> +
> ret = nfsd_svc(nrpools, nthreads, net, get_current_cred(), scope);
> if (ret > 0)
> ret = 0;
> @@ -1675,6 +1723,8 @@ int nfsd_nl_threads_get_doit(struct sk_buff *skb,
> struct genl_info *info)
> nn->nfsd4_grace) ||
> nla_put_u32(skb, NFSD_A_SERVER_LEASETIME,
> nn->nfsd4_lease) ||
> + nla_put_u32(skb, NFSD_A_SERVER_MIN_THREADS,
> + nn->min_threads) ||
> nla_put_string(skb, NFSD_A_SERVER_SCOPE,
> nn->nfsd_name);
> if (err)
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index
> 26c3a6cb1f400f1b757d26f6ba77e27deb7e8ee2..d6120dd843ac1b6a42f0ef331700f4d6d70d8c38
> 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, 0);
> + svc_set_num_threads(serv, 0, nn->min_threads);
Seems like this could actually /start/ threads during NFSD shutdown.
At the very least it needs an explanatory comment.
> 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], 0);
> + return svc_set_num_threads(nn->nfsd_serv, nthreads[0], nn->min_threads);
>
> 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], 0);
> + nthreads[i], nn->min_threads);
> 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, nn->min_threads);
> if (err)
> goto out;
> }
> diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> index
> 8885fd9bead98ebf55379d68ab9c3701981a5150..d1d0b0dd054588a8c20e3386356dfa4e9632b8e0
> 100644
> --- a/fs/nfsd/trace.h
> +++ b/fs/nfsd/trace.h
> @@ -2164,6 +2164,25 @@ TRACE_EVENT(nfsd_ctl_maxblksize,
> )
> );
>
> +TRACE_EVENT(nfsd_ctl_minthreads,
> + TP_PROTO(
> + const struct net *net,
> + int minthreads
> + ),
> + TP_ARGS(net, minthreads),
> + TP_STRUCT__entry(
> + __field(unsigned int, netns_ino)
> + __field(int, minthreads)
> + ),
> + TP_fast_assign(
> + __entry->netns_ino = net->ns.inum;
> + __entry->minthreads = minthreads
> + ),
> + TP_printk("minthreads=%d",
> + __entry->minthreads
> + )
> +);
> +
> TRACE_EVENT(nfsd_ctl_time,
> TP_PROTO(
> const struct net *net,
> diff --git a/include/uapi/linux/nfsd_netlink.h
> b/include/uapi/linux/nfsd_netlink.h
> index
> e157e2009ea8c1ef805301261d536c82677821ef..e9efbc9e63d83ed25fcd790b7a877c0023638f15
> 100644
> --- a/include/uapi/linux/nfsd_netlink.h
> +++ b/include/uapi/linux/nfsd_netlink.h
> @@ -35,6 +35,7 @@ enum {
> NFSD_A_SERVER_GRACETIME,
> NFSD_A_SERVER_LEASETIME,
> NFSD_A_SERVER_SCOPE,
> + NFSD_A_SERVER_MIN_THREADS,
>
> __NFSD_A_SERVER_MAX,
> NFSD_A_SERVER_MAX = (__NFSD_A_SERVER_MAX - 1)
>
> --
> 2.52.0
Thanks, Neil and Jeff, for pulling all this together. It's good to
have something we can noodle on now.
--
Chuck Lever
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