From 48be539dd44a3a010a6a330d09610d60ad42758a Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Fri, 4 May 2018 15:35:04 -0400 Subject: [PATCH] xprtrdma: Introduce ->alloc_slot call-out for xprtrdma rpcrdma_buffer_get acquires an rpcrdma_req and rep for each RPC. Currently this is done in the call_allocate action, and sometimes it can fail if there are many outstanding RPCs. When call_allocate fails, the RPC task is put on the delayq. It is awoken a few milliseconds later, but there's no guarantee it will get a buffer at that time. The RPC task can be repeatedly put back to sleep or even starved. The call_allocate action should rarely fail. The delayq mechanism is not meant to deal with transport congestion. In the current sunrpc stack, there is a friendlier way to deal with this situation. These objects are actually tantamount to an RPC slot (rpc_rqst) and there is a separate FSM action, distinct from call_allocate, for allocating slot resources. This is the call_reserve action. When allocation fails during this action, the RPC is placed on the transport's backlog queue. The backlog mechanism provides a stronger guarantee that when the RPC is awoken, a buffer will be available for it; and backlogged RPCs are awoken one-at-a-time. To make slot resource allocation occur in the call_reserve action, create special ->alloc_slot and ->free_slot call-outs for xprtrdma. Signed-off-by: Chuck Lever Signed-off-by: Anna Schumaker --- net/sunrpc/xprtrdma/transport.c | 52 +++++++++++++++++++++++++++++++-- 1 file changed, 50 insertions(+), 2 deletions(-) diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c index cf5e866ee969..8f9338e98c4f 100644 --- a/net/sunrpc/xprtrdma/transport.c +++ b/net/sunrpc/xprtrdma/transport.c @@ -538,6 +538,54 @@ xprt_rdma_connect(struct rpc_xprt *xprt, struct rpc_task *task) } } +/** + * xprt_rdma_alloc_slot - allocate an rpc_rqst + * @xprt: controlling RPC transport + * @task: RPC task requesting a fresh rpc_rqst + * + * tk_status values: + * %0 if task->tk_rqstp points to a fresh rpc_rqst + * %-EAGAIN if no rpc_rqst is available; queued on backlog + */ +static void +xprt_rdma_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task) +{ + struct rpc_rqst *rqst; + + spin_lock(&xprt->reserve_lock); + if (list_empty(&xprt->free)) + goto out_sleep; + rqst = list_first_entry(&xprt->free, struct rpc_rqst, rq_list); + list_del(&rqst->rq_list); + spin_unlock(&xprt->reserve_lock); + + task->tk_rqstp = rqst; + task->tk_status = 0; + return; + +out_sleep: + rpc_sleep_on(&xprt->backlog, task, NULL); + spin_unlock(&xprt->reserve_lock); + task->tk_status = -EAGAIN; +} + +/** + * xprt_rdma_free_slot - release an rpc_rqst + * @xprt: controlling RPC transport + * @rqst: rpc_rqst to release + * + */ +static void +xprt_rdma_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *rqst) +{ + memset(rqst, 0, sizeof(*rqst)); + + spin_lock(&xprt->reserve_lock); + list_add(&rqst->rq_list, &xprt->free); + rpc_wake_up_next(&xprt->backlog); + spin_unlock(&xprt->reserve_lock); +} + static bool rpcrdma_get_sendbuf(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req, size_t size, gfp_t flags) @@ -780,8 +828,8 @@ xprt_rdma_disable_swap(struct rpc_xprt *xprt) static const struct rpc_xprt_ops xprt_rdma_procs = { .reserve_xprt = xprt_reserve_xprt_cong, .release_xprt = xprt_release_xprt_cong, /* sunrpc/xprt.c */ - .alloc_slot = xprt_alloc_slot, - .free_slot = xprt_free_slot, + .alloc_slot = xprt_rdma_alloc_slot, + .free_slot = xprt_rdma_free_slot, .release_request = xprt_release_rqst_cong, /* ditto */ .set_retrans_timeout = xprt_set_retrans_timeout_def, /* ditto */ .timer = xprt_rdma_timer,