The patch looks good, just a couple notes to myself:
On Fri, Jun 24, 2016 at 10:55:50AM -0400, Trond Myklebust wrote:
> Allow the user to limit the number of requests serviced through a single
> connection.
>
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> ---
> Documentation/kernel-parameters.txt | 6 ++++++
> include/linux/sunrpc/svc.h | 1 +
> include/linux/sunrpc/svc_xprt.h | 1 +
> net/sunrpc/svc_xprt.c | 39 ++++++++++++++++++++++++++++++++++---
> 4 files changed, 44 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 82b42c958d1c..48ba6d2e670a 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -3832,6 +3832,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> using these two parameters to set the minimum and
> maximum port values.
>
> + sunrpc.svc_rpc_per_connection_limit=
> + [NFS,SUNRPC]
> + Limit the number of requests that the server will
> + process in parallel from a single connection.
> + The default value is 0 (no limit).
> +
Since every connection belongs to only one network namespace, we could
easily impose a different limit per network namespace. But module
parameters are stuck being global.
On the other hand, a module parameter may be simpler than the
alternatives, and we can always add a second interface later in the
unlikely event somebody cares about this, so.... OK.
> sunrpc.pool_mode=
> [NFS]
> Control how the NFS server code allocates CPUs to
> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> index 7ca44fb5b675..7321ae933867 100644
> --- a/include/linux/sunrpc/svc.h
> +++ b/include/linux/sunrpc/svc.h
> @@ -268,6 +268,7 @@ struct svc_rqst {
> * cache pages */
> #define RQ_VICTIM (5) /* about to be shut down */
> #define RQ_BUSY (6) /* request is busy */
> +#define RQ_DATA (7) /* request has data */
> unsigned long rq_flags; /* flags field */
>
> void * rq_argp; /* decoded arguments */
> diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
> index b7dabc4baafd..555c004de51e 100644
> --- a/include/linux/sunrpc/svc_xprt.h
> +++ b/include/linux/sunrpc/svc_xprt.h
> @@ -69,6 +69,7 @@ struct svc_xprt {
>
> struct svc_serv *xpt_server; /* service for transport */
> atomic_t xpt_reserved; /* space on outq that is rsvd */
> + atomic_t xpt_nr_rqsts; /* Number of requests */
> struct mutex xpt_mutex; /* to serialize sending data */
> spinlock_t xpt_lock; /* protects sk_deferred
> * and xpt_auth_cache */
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index eccc61237ca9..cd26d0d9e41f 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -21,6 +21,10 @@
>
> #define RPCDBG_FACILITY RPCDBG_SVCXPRT
>
> +static unsigned int svc_rpc_per_connection_limit __read_mostly;
> +module_param(svc_rpc_per_connection_limit, uint, 0644);
> +
> +
> static struct svc_deferred_req *svc_deferred_dequeue(struct svc_xprt *xprt);
> static int svc_deferred_recv(struct svc_rqst *rqstp);
> static struct cache_deferred_req *svc_defer(struct cache_req *req);
> @@ -327,12 +331,41 @@ char *svc_print_addr(struct svc_rqst *rqstp, char *buf, size_t len)
> }
> EXPORT_SYMBOL_GPL(svc_print_addr);
>
> +static bool svc_xprt_slots_in_range(struct svc_xprt *xprt)
> +{
> + unsigned int limit = svc_rpc_per_connection_limit;
> + int nrqsts = atomic_read(&xprt->xpt_nr_rqsts);
> +
> + return limit == 0 || (nrqsts >= 0 && nrqsts < limit);
> +}
> +
> +static bool svc_xprt_reserve_slot(struct svc_rqst *rqstp, struct svc_xprt *xprt)
> +{
> + if (!test_bit(RQ_DATA, &rqstp->rq_flags)) {
> + if (!svc_xprt_slots_in_range(xprt))
> + return false;
> + atomic_inc(&xprt->xpt_nr_rqsts);
> + set_bit(RQ_DATA, &rqstp->rq_flags);
The separate test_bit() and set_bit() had me scratching my head for a
moment.... OK, all of the RQ_DATA uses are only from the unique thread
associated with this rqstp, so there should be no races (and the
test_and_clear_bit() below is just for convenience, I guess, we don't
really need it to be atomic).
--b.
> + }
> + return true;
> +}
> +
> +static void svc_xprt_release_slot(struct svc_rqst *rqstp)
> +{
> + struct svc_xprt *xprt = rqstp->rq_xprt;
> + if (test_and_clear_bit(RQ_DATA, &rqstp->rq_flags)) {
> + atomic_dec(&xprt->xpt_nr_rqsts);
> + svc_xprt_enqueue(xprt);
> + }
> +}
> +
> static bool svc_xprt_has_something_to_do(struct svc_xprt *xprt)
> {
> if (xprt->xpt_flags & ((1<<XPT_CONN)|(1<<XPT_CLOSE)))
> return true;
> if (xprt->xpt_flags & ((1<<XPT_DATA)|(1<<XPT_DEFERRED))) {
> - if (xprt->xpt_ops->xpo_has_wspace(xprt))
> + if (xprt->xpt_ops->xpo_has_wspace(xprt) &&
> + svc_xprt_slots_in_range(xprt))
> return true;
> trace_svc_xprt_no_write_space(xprt);
> return false;
> @@ -514,8 +547,8 @@ static void svc_xprt_release(struct svc_rqst *rqstp)
>
> rqstp->rq_res.head[0].iov_len = 0;
> svc_reserve(rqstp, 0);
> + svc_xprt_release_slot(rqstp);
> rqstp->rq_xprt = NULL;
> -
> svc_xprt_put(xprt);
> }
>
> @@ -783,7 +816,7 @@ static int svc_handle_xprt(struct svc_rqst *rqstp, struct svc_xprt *xprt)
> svc_add_new_temp_xprt(serv, newxpt);
> else
> module_put(xprt->xpt_class->xcl_owner);
> - } else {
> + } else if (svc_xprt_reserve_slot(rqstp, xprt)) {
> /* XPT_DATA|XPT_DEFERRED case: */
> dprintk("svc: server %p, pool %u, transport %p, inuse=%d\n",
> rqstp, rqstp->rq_pool->sp_id, xprt,
> --
> 2.7.4
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