xprtrdma: Allocate MRs on demand

Frequent MR list exhaustion can impact I/O throughput, so enough MRs
are always created during transport set-up to prevent running out.
This means more MRs are created than most workloads need.

Commit 94f58c58c0b4 ("xprtrdma: Allow Read list and Reply chunk
simultaneously") introduced support for sending two chunk lists per
RPC, which consumes more MRs per RPC.

Instead of trying to provision more MRs, introduce a mechanism for
allocating MRs on demand. A few MRs are allocated during transport
set-up to kick things off.

This significantly reduces the average number of MRs per transport
while allowing the MR count to grow for workloads or devices that
need more MRs.

FRWR with mlx4 allocated almost 400 MRs per transport before this
patch. Now it starts with 32.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/fmr_ops.c

@@ -46,7 +46,7 @@ fmr_is_supported(struct rpcrdma_ia *ia)
 }
 
 static int
-__fmr_init(struct rpcrdma_mw *mw, struct ib_pd *pd)
+fmr_op_init_mr(struct rpcrdma_ia *ia, struct rpcrdma_mw *mw)
 {
 	static struct ib_fmr_attr fmr_attr = {
 		.max_pages	= RPCRDMA_MAX_FMR_SGES,
@@ -66,7 +66,7 @@ __fmr_init(struct rpcrdma_mw *mw, struct ib_pd *pd)
 
 	sg_init_table(mw->mw_sg, RPCRDMA_MAX_FMR_SGES);
 
-	mw->fmr.fm_mr = ib_alloc_fmr(pd, RPCRDMA_FMR_ACCESS_FLAGS,
+	mw->fmr.fm_mr = ib_alloc_fmr(ia->ri_pd, RPCRDMA_FMR_ACCESS_FLAGS,
 				     &fmr_attr);
 	if (IS_ERR(mw->fmr.fm_mr))
 		goto out_fmr_err;
@@ -96,7 +96,7 @@ __fmr_unmap(struct rpcrdma_mw *mw)
 }
 
 static void
-__fmr_release(struct rpcrdma_mw *r)
+fmr_op_release_mr(struct rpcrdma_mw *r)
 {
 	LIST_HEAD(unmap_list);
 	int rc;
@@ -116,13 +116,11 @@ __fmr_release(struct rpcrdma_mw *r)
 	if (rc)
 		pr_err("rpcrdma: final ib_dealloc_fmr for %p returned %i\n",
 		       r, rc);
+
+	kfree(r);
 }
 
 /* Reset of a single FMR.
- *
- * There's no recovery if this fails. The FMR is abandoned, but
- * remains in rb_all. It will be cleaned up when the transport is
- * destroyed.
  */
 static void
 fmr_op_recover_mr(struct rpcrdma_mw *mw)
@@ -166,41 +164,6 @@ fmr_op_maxpages(struct rpcrdma_xprt *r_xprt)
 		     RPCRDMA_MAX_HDR_SEGS * RPCRDMA_MAX_FMR_SGES);
 }
 
-static int
-fmr_op_init(struct rpcrdma_xprt *r_xprt)
-{
-	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
-	struct ib_pd *pd = r_xprt->rx_ia.ri_pd;
-	struct rpcrdma_mw *r;
-	int i, rc;
-
-	spin_lock_init(&buf->rb_mwlock);
-	INIT_LIST_HEAD(&buf->rb_mws);
-	INIT_LIST_HEAD(&buf->rb_all);
-
-	i = max_t(int, RPCRDMA_MAX_DATA_SEGS / RPCRDMA_MAX_FMR_SGES, 1);
-	i += 2;				/* head + tail */
-	i *= buf->rb_max_requests;	/* one set for each RPC slot */
-	dprintk("RPC:       %s: initalizing %d FMRs\n", __func__, i);
-
-	while (i--) {
-		r = kzalloc(sizeof(*r), GFP_KERNEL);
-		if (!r)
-			return -ENOMEM;
-
-		rc = __fmr_init(r, pd);
-		if (rc) {
-			kfree(r);
-			return rc;
-		}
-
-		r->mw_xprt = r_xprt;
-		list_add(&r->mw_list, &buf->rb_mws);
-		list_add(&r->mw_all, &buf->rb_all);
-	}
-	return 0;
-}
-
 /* Use the ib_map_phys_fmr() verb to register a memory region
  * for remote access via RDMA READ or RDMA WRITE.
  */
@@ -374,19 +337,6 @@ fmr_op_unmap_safe(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req,
 	}
 }
 
-static void
-fmr_op_destroy(struct rpcrdma_buffer *buf)
-{
-	struct rpcrdma_mw *r;
-
-	while (!list_empty(&buf->rb_all)) {
-		r = list_entry(buf->rb_all.next, struct rpcrdma_mw, mw_all);
-		list_del(&r->mw_all);
-		__fmr_release(r);
-		kfree(r);
-	}
-}
-
 const struct rpcrdma_memreg_ops rpcrdma_fmr_memreg_ops = {
 	.ro_map				= fmr_op_map,
 	.ro_unmap_sync			= fmr_op_unmap_sync,
@@ -394,7 +344,7 @@ const struct rpcrdma_memreg_ops rpcrdma_fmr_memreg_ops = {
 	.ro_recover_mr			= fmr_op_recover_mr,
 	.ro_open			= fmr_op_open,
 	.ro_maxpages			= fmr_op_maxpages,
-	.ro_init			= fmr_op_init,
-	.ro_destroy			= fmr_op_destroy,
+	.ro_init_mr			= fmr_op_init_mr,
+	.ro_release_mr			= fmr_op_release_mr,
 	.ro_displayname			= "fmr",
 };

net/sunrpc/xprtrdma/frwr_ops.c

@@ -91,12 +91,13 @@ out_not_supported:
 }
 
 static int
-__frwr_init(struct rpcrdma_mw *r, struct ib_pd *pd, unsigned int depth)
+frwr_op_init_mr(struct rpcrdma_ia *ia, struct rpcrdma_mw *r)
 {
+	unsigned int depth = ia->ri_max_frmr_depth;
 	struct rpcrdma_frmr *f = &r->frmr;
 	int rc;
 
-	f->fr_mr = ib_alloc_mr(pd, IB_MR_TYPE_MEM_REG, depth);
+	f->fr_mr = ib_alloc_mr(ia->ri_pd, IB_MR_TYPE_MEM_REG, depth);
 	if (IS_ERR(f->fr_mr))
 		goto out_mr_err;
 
@@ -123,7 +124,7 @@ out_list_err:
 }
 
 static void
-__frwr_release(struct rpcrdma_mw *r)
+frwr_op_release_mr(struct rpcrdma_mw *r)
 {
 	int rc;
 
@@ -132,6 +133,7 @@ __frwr_release(struct rpcrdma_mw *r)
 		pr_err("rpcrdma: final ib_dereg_mr for %p returned %i\n",
 		       r, rc);
 	kfree(r->mw_sg);
+	kfree(r);
 }
 
 static int
@@ -319,45 +321,6 @@ frwr_wc_localinv_wake(struct ib_cq *cq, struct ib_wc *wc)
 	complete_all(&frmr->fr_linv_done);
 }
 
-static int
-frwr_op_init(struct rpcrdma_xprt *r_xprt)
-{
-	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
-	unsigned int depth = r_xprt->rx_ia.ri_max_frmr_depth;
-	struct ib_pd *pd = r_xprt->rx_ia.ri_pd;
-	int i;
-
-	spin_lock_init(&buf->rb_mwlock);
-	INIT_LIST_HEAD(&buf->rb_mws);
-	INIT_LIST_HEAD(&buf->rb_all);
-
-	i = max_t(int, RPCRDMA_MAX_DATA_SEGS / depth, 1);
-	i += 2;				/* head + tail */
-	i *= buf->rb_max_requests;	/* one set for each RPC slot */
-	dprintk("RPC:       %s: initalizing %d FRMRs\n", __func__, i);
-
-	while (i--) {
-		struct rpcrdma_mw *r;
-		int rc;
-
-		r = kzalloc(sizeof(*r), GFP_KERNEL);
-		if (!r)
-			return -ENOMEM;
-
-		rc = __frwr_init(r, pd, depth);
-		if (rc) {
-			kfree(r);
-			return rc;
-		}
-
-		r->mw_xprt = r_xprt;
-		list_add(&r->mw_list, &buf->rb_mws);
-		list_add(&r->mw_all, &buf->rb_all);
-	}
-
-	return 0;
-}
-
 /* Post a REG_MR Work Request to register a memory region
  * for remote access via RDMA READ or RDMA WRITE.
  */
@@ -618,19 +581,6 @@ frwr_op_unmap_safe(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req,
 	}
 }
 
-static void
-frwr_op_destroy(struct rpcrdma_buffer *buf)
-{
-	struct rpcrdma_mw *r;
-
-	while (!list_empty(&buf->rb_all)) {
-		r = list_entry(buf->rb_all.next, struct rpcrdma_mw, mw_all);
-		list_del(&r->mw_all);
-		__frwr_release(r);
-		kfree(r);
-	}
-}
-
 const struct rpcrdma_memreg_ops rpcrdma_frwr_memreg_ops = {
 	.ro_map				= frwr_op_map,
 	.ro_unmap_sync			= frwr_op_unmap_sync,
@@ -638,7 +588,7 @@ const struct rpcrdma_memreg_ops rpcrdma_frwr_memreg_ops = {
 	.ro_recover_mr			= frwr_op_recover_mr,
 	.ro_open			= frwr_op_open,
 	.ro_maxpages			= frwr_op_maxpages,
-	.ro_init			= frwr_op_init,
-	.ro_destroy			= frwr_op_destroy,
+	.ro_init_mr			= frwr_op_init_mr,
+	.ro_release_mr			= frwr_op_release_mr,
 	.ro_displayname			= "frwr",
 };

net/sunrpc/xprtrdma/transport.c

@@ -682,9 +682,10 @@ void xprt_rdma_print_stats(struct rpc_xprt *xprt, struct seq_file *seq)
 		   r_xprt->rx_stats.failed_marshal_count,
 		   r_xprt->rx_stats.bad_reply_count,
 		   r_xprt->rx_stats.nomsg_call_count);
-	seq_printf(seq, "%lu %lu\n",
+	seq_printf(seq, "%lu %lu %lu\n",
 		   r_xprt->rx_stats.mrs_recovered,
-		   r_xprt->rx_stats.mrs_orphaned);
+		   r_xprt->rx_stats.mrs_orphaned,
+		   r_xprt->rx_stats.mrs_allocated);
 }
 
 static int

net/sunrpc/xprtrdma/verbs.c

@@ -782,6 +782,55 @@ rpcrdma_defer_mr_recovery(struct rpcrdma_mw *mw)
 	schedule_delayed_work(&buf->rb_recovery_worker, 0);
 }
 
+static void
+rpcrdma_create_mrs(struct rpcrdma_xprt *r_xprt)
+{
+	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
+	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
+	unsigned int count;
+	LIST_HEAD(free);
+	LIST_HEAD(all);
+
+	for (count = 0; count < 32; count++) {
+		struct rpcrdma_mw *mw;
+		int rc;
+
+		mw = kzalloc(sizeof(*mw), GFP_KERNEL);
+		if (!mw)
+			break;
+
+		rc = ia->ri_ops->ro_init_mr(ia, mw);
+		if (rc) {
+			kfree(mw);
+			break;
+		}
+
+		mw->mw_xprt = r_xprt;
+
+		list_add(&mw->mw_list, &free);
+		list_add(&mw->mw_all, &all);
+	}
+
+	spin_lock(&buf->rb_mwlock);
+	list_splice(&free, &buf->rb_mws);
+	list_splice(&all, &buf->rb_all);
+	r_xprt->rx_stats.mrs_allocated += count;
+	spin_unlock(&buf->rb_mwlock);
+
+	dprintk("RPC:       %s: created %u MRs\n", __func__, count);
+}
+
+static void
+rpcrdma_mr_refresh_worker(struct work_struct *work)
+{
+	struct rpcrdma_buffer *buf = container_of(work, struct rpcrdma_buffer,
+						  rb_refresh_worker.work);
+	struct rpcrdma_xprt *r_xprt = container_of(buf, struct rpcrdma_xprt,
+						   rx_buf);
+
+	rpcrdma_create_mrs(r_xprt);
+}
+
 struct rpcrdma_req *
 rpcrdma_create_req(struct rpcrdma_xprt *r_xprt)
 {
@@ -837,21 +886,23 @@ int
 rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt)
 {
 	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
-	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
 	int i, rc;
 
 	buf->rb_max_requests = r_xprt->rx_data.max_requests;
 	buf->rb_bc_srv_max_requests = 0;
 	atomic_set(&buf->rb_credits, 1);
+	spin_lock_init(&buf->rb_mwlock);
 	spin_lock_init(&buf->rb_lock);
 	spin_lock_init(&buf->rb_recovery_lock);
+	INIT_LIST_HEAD(&buf->rb_mws);
+	INIT_LIST_HEAD(&buf->rb_all);
 	INIT_LIST_HEAD(&buf->rb_stale_mrs);
+	INIT_DELAYED_WORK(&buf->rb_refresh_worker,
+			  rpcrdma_mr_refresh_worker);
 	INIT_DELAYED_WORK(&buf->rb_recovery_worker,
 			  rpcrdma_mr_recovery_worker);
 
-	rc = ia->ri_ops->ro_init(r_xprt);
-	if (rc)
-		goto out;
+	rpcrdma_create_mrs(r_xprt);
 
 	INIT_LIST_HEAD(&buf->rb_send_bufs);
 	INIT_LIST_HEAD(&buf->rb_allreqs);
@@ -927,6 +978,32 @@ rpcrdma_destroy_req(struct rpcrdma_ia *ia, struct rpcrdma_req *req)
 	kfree(req);
 }
 
+static void
+rpcrdma_destroy_mrs(struct rpcrdma_buffer *buf)
+{
+	struct rpcrdma_xprt *r_xprt = container_of(buf, struct rpcrdma_xprt,
+						   rx_buf);
+	struct rpcrdma_ia *ia = rdmab_to_ia(buf);
+	struct rpcrdma_mw *mw;
+	unsigned int count;
+
+	count = 0;
+	spin_lock(&buf->rb_mwlock);
+	while (!list_empty(&buf->rb_all)) {
+		mw = list_entry(buf->rb_all.next, struct rpcrdma_mw, mw_all);
+		list_del(&mw->mw_all);
+
+		spin_unlock(&buf->rb_mwlock);
+		ia->ri_ops->ro_release_mr(mw);
+		count++;
+		spin_lock(&buf->rb_mwlock);
+	}
+	spin_unlock(&buf->rb_mwlock);
+	r_xprt->rx_stats.mrs_allocated = 0;
+
+	dprintk("RPC:       %s: released %u MRs\n", __func__, count);
+}
+
 void
 rpcrdma_buffer_destroy(struct rpcrdma_buffer *buf)
 {
@@ -955,7 +1032,7 @@ rpcrdma_buffer_destroy(struct rpcrdma_buffer *buf)
 	}
 	spin_unlock(&buf->rb_reqslock);
 
-	ia->ri_ops->ro_destroy(buf);
+	rpcrdma_destroy_mrs(buf);
 }
 
 struct rpcrdma_mw *
@@ -973,8 +1050,17 @@ rpcrdma_get_mw(struct rpcrdma_xprt *r_xprt)
 	spin_unlock(&buf->rb_mwlock);
 
 	if (!mw)
-		pr_err("RPC:       %s: no MWs available\n", __func__);
+		goto out_nomws;
 	return mw;
+
+out_nomws:
+	dprintk("RPC:       %s: no MWs available\n", __func__);
+	schedule_delayed_work(&buf->rb_refresh_worker, 0);
+
+	/* Allow the reply handler and refresh worker to run */
+	cond_resched();
+
+	return NULL;
 }
 
 void

net/sunrpc/xprtrdma/xprt_rdma.h

@@ -339,6 +339,7 @@ struct rpcrdma_buffer {
 	spinlock_t		rb_recovery_lock; /* protect rb_stale_mrs */
 	struct list_head	rb_stale_mrs;
 	struct delayed_work	rb_recovery_worker;
+	struct delayed_work	rb_refresh_worker;
 };
 #define rdmab_to_ia(b) (&container_of((b), struct rpcrdma_xprt, rx_buf)->rx_ia)
 
@@ -387,6 +388,7 @@ struct rpcrdma_stats {
 	unsigned long		bcall_count;
 	unsigned long		mrs_recovered;
 	unsigned long		mrs_orphaned;
+	unsigned long		mrs_allocated;
 };
 
 /*
@@ -405,8 +407,9 @@ struct rpcrdma_memreg_ops {
 				   struct rpcrdma_ep *,
 				   struct rpcrdma_create_data_internal *);
 	size_t		(*ro_maxpages)(struct rpcrdma_xprt *);
-	int		(*ro_init)(struct rpcrdma_xprt *);
-	void		(*ro_destroy)(struct rpcrdma_buffer *);
+	int		(*ro_init_mr)(struct rpcrdma_ia *,
+				      struct rpcrdma_mw *);
+	void		(*ro_release_mr)(struct rpcrdma_mw *);
 	const char	*ro_displayname;
 };