svcrdma: Change WR context get/put to use the kmem cache

Change the WR context pool to be shared across mount points. This
reduces the RDMA transport memory footprint significantly since
idle mounts don't consume WR context memory.
Signed-off-by: Tom Tucker <tom@opengridcomputing.com>

include/linux/sunrpc/svc_rdma.h

@@ -73,7 +73,6 @@ extern atomic_t rdma_stat_sq_prod;
 struct svc_rdma_op_ctxt {
 	struct svc_rdma_op_ctxt *read_hdr;
 	int hdr_count;
-	struct list_head free_list;
 	struct xdr_buf arg;
 	struct list_head dto_q;
 	enum ib_wr_opcode wr_op;
@@ -131,11 +130,6 @@ struct svcxprt_rdma {
 
 	atomic_t	     sc_dma_used;
 	atomic_t	     sc_ctxt_used;
-	struct list_head     sc_ctxt_free;
-	int		     sc_ctxt_cnt;
-	int		     sc_ctxt_bump;
-	int		     sc_ctxt_max;
-	spinlock_t	     sc_ctxt_lock;
 	struct list_head     sc_rq_dto_q;
 	spinlock_t	     sc_rq_dto_lock;
 	struct ib_qp         *sc_qp;

net/sunrpc/xprtrdma/svc_rdma_transport.c

@@ -84,69 +84,23 @@ struct svc_xprt_class svc_rdma_class = {
 	.xcl_max_payload = RPCSVC_MAXPAYLOAD_TCP,
 };
 
-static int rdma_bump_context_cache(struct svcxprt_rdma *xprt)
-{
-	int target;
-	int at_least_one = 0;
-	struct svc_rdma_op_ctxt *ctxt;
-
-	target = min(xprt->sc_ctxt_cnt + xprt->sc_ctxt_bump,
-		     xprt->sc_ctxt_max);
-
-	spin_lock_bh(&xprt->sc_ctxt_lock);
-	while (xprt->sc_ctxt_cnt < target) {
-		xprt->sc_ctxt_cnt++;
-		spin_unlock_bh(&xprt->sc_ctxt_lock);
-
-		ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
-
-		spin_lock_bh(&xprt->sc_ctxt_lock);
-		if (ctxt) {
-			at_least_one = 1;
-			INIT_LIST_HEAD(&ctxt->free_list);
-			list_add(&ctxt->free_list, &xprt->sc_ctxt_free);
-		} else {
-			/* kmalloc failed...give up for now */
-			xprt->sc_ctxt_cnt--;
-			break;
-		}
-	}
-	spin_unlock_bh(&xprt->sc_ctxt_lock);
-	dprintk("svcrdma: sc_ctxt_max=%d, sc_ctxt_cnt=%d\n",
-		xprt->sc_ctxt_max, xprt->sc_ctxt_cnt);
-	return at_least_one;
-}
+/* WR context cache. Created in svc_rdma.c  */
+extern struct kmem_cache *svc_rdma_ctxt_cachep;
 
 struct svc_rdma_op_ctxt *svc_rdma_get_context(struct svcxprt_rdma *xprt)
 {
 	struct svc_rdma_op_ctxt *ctxt;
 
 	while (1) {
-		spin_lock_bh(&xprt->sc_ctxt_lock);
-		if (unlikely(list_empty(&xprt->sc_ctxt_free))) {
-			/* Try to bump my cache. */
-			spin_unlock_bh(&xprt->sc_ctxt_lock);
-
-			if (rdma_bump_context_cache(xprt))
-				continue;
-
-			printk(KERN_INFO "svcrdma: sleeping waiting for "
-			       "context memory on xprt=%p\n",
-			       xprt);
-			schedule_timeout_uninterruptible(msecs_to_jiffies(500));
-			continue;
-		}
-		ctxt = list_entry(xprt->sc_ctxt_free.next,
-				  struct svc_rdma_op_ctxt,
-				  free_list);
-		list_del_init(&ctxt->free_list);
-		spin_unlock_bh(&xprt->sc_ctxt_lock);
-		ctxt->xprt = xprt;
-		INIT_LIST_HEAD(&ctxt->dto_q);
-		ctxt->count = 0;
-		atomic_inc(&xprt->sc_ctxt_used);
-		break;
+		ctxt = kmem_cache_alloc(svc_rdma_ctxt_cachep, GFP_KERNEL);
+		if (ctxt)
+			break;
+		schedule_timeout_uninterruptible(msecs_to_jiffies(500));
 	}
+	ctxt->xprt = xprt;
+	INIT_LIST_HEAD(&ctxt->dto_q);
+	ctxt->count = 0;
+	atomic_inc(&xprt->sc_ctxt_used);
 	return ctxt;
 }
 
@@ -174,9 +128,7 @@ void svc_rdma_put_context(struct svc_rdma_op_ctxt *ctxt, int free_pages)
 		for (i = 0; i < ctxt->count; i++)
 			put_page(ctxt->pages[i]);
 
-	spin_lock_bh(&xprt->sc_ctxt_lock);
-	list_add(&ctxt->free_list, &xprt->sc_ctxt_free);
-	spin_unlock_bh(&xprt->sc_ctxt_lock);
+	kmem_cache_free(svc_rdma_ctxt_cachep, ctxt);
 	atomic_dec(&xprt->sc_ctxt_used);
 }
 
@@ -461,40 +413,6 @@ static void sq_comp_handler(struct ib_cq *cq, void *cq_context)
 	tasklet_schedule(&dto_tasklet);
 }
 
-static void create_context_cache(struct svcxprt_rdma *xprt,
-				 int ctxt_count, int ctxt_bump, int ctxt_max)
-{
-	struct svc_rdma_op_ctxt *ctxt;
-	int i;
-
-	xprt->sc_ctxt_max = ctxt_max;
-	xprt->sc_ctxt_bump = ctxt_bump;
-	xprt->sc_ctxt_cnt = 0;
-	atomic_set(&xprt->sc_ctxt_used, 0);
-
-	INIT_LIST_HEAD(&xprt->sc_ctxt_free);
-	for (i = 0; i < ctxt_count; i++) {
-		ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
-		if (ctxt) {
-			INIT_LIST_HEAD(&ctxt->free_list);
-			list_add(&ctxt->free_list, &xprt->sc_ctxt_free);
-			xprt->sc_ctxt_cnt++;
-		}
-	}
-}
-
-static void destroy_context_cache(struct svcxprt_rdma *xprt)
-{
-	while (!list_empty(&xprt->sc_ctxt_free)) {
-		struct svc_rdma_op_ctxt *ctxt;
-		ctxt = list_entry(xprt->sc_ctxt_free.next,
-				  struct svc_rdma_op_ctxt,
-				  free_list);
-		list_del_init(&ctxt->free_list);
-		kfree(ctxt);
-	}
-}
-
 static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
 					     int listener)
 {
@@ -511,7 +429,6 @@ static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
 
 	spin_lock_init(&cma_xprt->sc_lock);
 	spin_lock_init(&cma_xprt->sc_read_complete_lock);
-	spin_lock_init(&cma_xprt->sc_ctxt_lock);
 	spin_lock_init(&cma_xprt->sc_rq_dto_lock);
 
 	cma_xprt->sc_ord = svcrdma_ord;
@@ -522,20 +439,7 @@ static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
 	atomic_set(&cma_xprt->sc_sq_count, 0);
 	atomic_set(&cma_xprt->sc_ctxt_used, 0);
 
-	if (!listener) {
-		int reqs = cma_xprt->sc_max_requests;
-		create_context_cache(cma_xprt,
-				     reqs << 1, /* starting size */
-				     reqs,	/* bump amount */
-				     reqs +
-				     cma_xprt->sc_sq_depth +
-				     RPCRDMA_MAX_THREADS + 1); /* max */
-		if (list_empty(&cma_xprt->sc_ctxt_free)) {
-			kfree(cma_xprt);
-			return NULL;
-		}
-		clear_bit(XPT_LISTENER, &cma_xprt->sc_xprt.xpt_flags);
-	} else
+	if (listener)
 		set_bit(XPT_LISTENER, &cma_xprt->sc_xprt.xpt_flags);
 
 	return cma_xprt;
@@ -1077,7 +981,6 @@ static void __svc_rdma_free(struct work_struct *work)
 	/* Destroy the CM ID */
 	rdma_destroy_id(rdma->sc_cm_id);
 
-	destroy_context_cache(rdma);
 	kfree(rdma);
 }