[PATCH v2 2/2] vhost: stop using mempool for IOTLB cache

[David Marchand <david.marchand@redhat.com>]

A mempool consumes 3 memzones (with the default ring mempool driver).
The default DPDK configuration allows RTE_MAX_MEMZONE (2560) memzones.

Assuming there is no other memzones that means that we can have a
maximum of 853 mempools.

In the vhost library, the IOTLB cache code so far was requesting a
mempool per vq, which means that at the maximum, the vhost library
could request mempools for 426 qps.

This limit was recently reached on big systems with a lot of virtio
ports (and multiqueue in use).

While the limit on mempool count could be something we fix at the DPDK
project level, there is no reason to use mempools for the IOTLB cache:
- the IOTLB cache entries do not need to be DMA-able and are only used
  by the current process (in multiprocess context),
- getting/putting objects from/in the mempool is always associated with
  some other locks, so some level of lock contention is already present,

We can convert to a malloc'd pool with objects put in a free list
protected by a spinlock.

Signed-off-by: David Marchand <david.marchand@redhat.com>
---
 lib/vhost/iotlb.c | 102 ++++++++++++++++++++++++++++------------------
 lib/vhost/iotlb.h |   1 +
 lib/vhost/vhost.c |   2 +-
 lib/vhost/vhost.h |   4 +-
 4 files changed, 67 insertions(+), 42 deletions(-)

diff --git a/lib/vhost/iotlb.c b/lib/vhost/iotlb.c
index dd35338ec0..2a78929e78 100644
--- a/lib/vhost/iotlb.c
+++ b/lib/vhost/iotlb.c
@@ -13,6 +13,7 @@
 
 struct vhost_iotlb_entry {
 	TAILQ_ENTRY(vhost_iotlb_entry) next;
+	SLIST_ENTRY(vhost_iotlb_entry) next_free;
 
 	uint64_t iova;
 	uint64_t uaddr;
@@ -22,6 +23,28 @@ struct vhost_iotlb_entry {
 
 #define IOTLB_CACHE_SIZE 2048
 
+static struct vhost_iotlb_entry *
+vhost_user_iotlb_pool_get(struct vhost_virtqueue *vq)
+{
+	struct vhost_iotlb_entry *node;
+
+	rte_spinlock_lock(&vq->iotlb_free_lock);
+	node = SLIST_FIRST(&vq->iotlb_free_list);
+	if (node != NULL)
+		SLIST_REMOVE_HEAD(&vq->iotlb_free_list, next_free);
+	rte_spinlock_unlock(&vq->iotlb_free_lock);
+	return node;
+}
+
+static void
+vhost_user_iotlb_pool_put(struct vhost_virtqueue *vq,
+	struct vhost_iotlb_entry *node)
+{
+	rte_spinlock_lock(&vq->iotlb_free_lock);
+	SLIST_INSERT_HEAD(&vq->iotlb_free_list, node, next_free);
+	rte_spinlock_unlock(&vq->iotlb_free_lock);
+}
+
 static void
 vhost_user_iotlb_cache_random_evict(struct vhost_virtqueue *vq);
 
@@ -34,7 +57,7 @@ vhost_user_iotlb_pending_remove_all(struct vhost_virtqueue *vq)
 
 	RTE_TAILQ_FOREACH_SAFE(node, &vq->iotlb_pending_list, next, temp_node) {
 		TAILQ_REMOVE(&vq->iotlb_pending_list, node, next);
-		rte_mempool_put(vq->iotlb_pool, node);
+		vhost_user_iotlb_pool_put(vq, node);
 	}
 
 	rte_rwlock_write_unlock(&vq->iotlb_pending_lock);
@@ -66,22 +89,21 @@ vhost_user_iotlb_pending_insert(struct virtio_net *dev, struct vhost_virtqueue *
 				uint64_t iova, uint8_t perm)
 {
 	struct vhost_iotlb_entry *node;
-	int ret;
 
-	ret = rte_mempool_get(vq->iotlb_pool, (void **)&node);
-	if (ret) {
+	node = vhost_user_iotlb_pool_get(vq);
+	if (node == NULL) {
 		VHOST_LOG_CONFIG(dev->ifname, DEBUG,
-			"IOTLB pool %s empty, clear entries for pending insertion\n",
-			vq->iotlb_pool->name);
+			"IOTLB pool for vq %"PRIu32" empty, clear entries for pending insertion\n",
+			vq->index);
 		if (!TAILQ_EMPTY(&vq->iotlb_pending_list))
 			vhost_user_iotlb_pending_remove_all(vq);
 		else
 			vhost_user_iotlb_cache_random_evict(vq);
-		ret = rte_mempool_get(vq->iotlb_pool, (void **)&node);
-		if (ret) {
+		node = vhost_user_iotlb_pool_get(vq);
+		if (node == NULL) {
 			VHOST_LOG_CONFIG(dev->ifname, ERR,
-				"IOTLB pool %s still empty, pending insertion failure\n",
-				vq->iotlb_pool->name);
+				"IOTLB pool vq %"PRIu32" still empty, pending insertion failure\n",
+				vq->index);
 			return;
 		}
 	}
@@ -113,7 +135,7 @@ vhost_user_iotlb_pending_remove(struct vhost_virtqueue *vq,
 		if ((node->perm & perm) != node->perm)
 			continue;
 		TAILQ_REMOVE(&vq->iotlb_pending_list, node, next);
-		rte_mempool_put(vq->iotlb_pool, node);
+		vhost_user_iotlb_pool_put(vq, node);
 	}
 
 	rte_rwlock_write_unlock(&vq->iotlb_pending_lock);
@@ -128,7 +150,7 @@ vhost_user_iotlb_cache_remove_all(struct vhost_virtqueue *vq)
 
 	RTE_TAILQ_FOREACH_SAFE(node, &vq->iotlb_list, next, temp_node) {
 		TAILQ_REMOVE(&vq->iotlb_list, node, next);
-		rte_mempool_put(vq->iotlb_pool, node);
+		vhost_user_iotlb_pool_put(vq, node);
 	}
 
 	vq->iotlb_cache_nr = 0;
@@ -149,7 +171,7 @@ vhost_user_iotlb_cache_random_evict(struct vhost_virtqueue *vq)
 	RTE_TAILQ_FOREACH_SAFE(node, &vq->iotlb_list, next, temp_node) {
 		if (!entry_idx) {
 			TAILQ_REMOVE(&vq->iotlb_list, node, next);
-			rte_mempool_put(vq->iotlb_pool, node);
+			vhost_user_iotlb_pool_put(vq, node);
 			vq->iotlb_cache_nr--;
 			break;
 		}
@@ -165,22 +187,21 @@ vhost_user_iotlb_cache_insert(struct virtio_net *dev, struct vhost_virtqueue *vq
 				uint64_t size, uint8_t perm)
 {
 	struct vhost_iotlb_entry *node, *new_node;
-	int ret;
 
-	ret = rte_mempool_get(vq->iotlb_pool, (void **)&new_node);
-	if (ret) {
+	new_node = vhost_user_iotlb_pool_get(vq);
+	if (new_node == NULL) {
 		VHOST_LOG_CONFIG(dev->ifname, DEBUG,
-			"IOTLB pool %s empty, clear entries for cache insertion\n",
-			vq->iotlb_pool->name);
+			"IOTLB pool vq %"PRIu32" empty, clear entries for cache insertion\n",
+			vq->index);
 		if (!TAILQ_EMPTY(&vq->iotlb_list))
 			vhost_user_iotlb_cache_random_evict(vq);
 		else
 			vhost_user_iotlb_pending_remove_all(vq);
-		ret = rte_mempool_get(vq->iotlb_pool, (void **)&new_node);
-		if (ret) {
+		new_node = vhost_user_iotlb_pool_get(vq);
+		if (new_node == NULL) {
 			VHOST_LOG_CONFIG(dev->ifname, ERR,
-				"IOTLB pool %s still empty, cache insertion failed\n",
-				vq->iotlb_pool->name);
+				"IOTLB pool vq %"PRIu32" still empty, cache insertion failed\n",
+				vq->index);
 			return;
 		}
 	}
@@ -198,7 +219,7 @@ vhost_user_iotlb_cache_insert(struct virtio_net *dev, struct vhost_virtqueue *vq
 		 * So if iova already in list, assume identical.
 		 */
 		if (node->iova == new_node->iova) {
-			rte_mempool_put(vq->iotlb_pool, new_node);
+			vhost_user_iotlb_pool_put(vq, new_node);
 			goto unlock;
 		} else if (node->iova > new_node->iova) {
 			TAILQ_INSERT_BEFORE(node, new_node, next);
@@ -235,7 +256,7 @@ vhost_user_iotlb_cache_remove(struct vhost_virtqueue *vq,
 
 		if (iova < node->iova + node->size) {
 			TAILQ_REMOVE(&vq->iotlb_list, node, next);
-			rte_mempool_put(vq->iotlb_pool, node);
+			vhost_user_iotlb_pool_put(vq, node);
 			vq->iotlb_cache_nr--;
 		}
 	}
@@ -295,7 +316,7 @@ vhost_user_iotlb_flush_all(struct vhost_virtqueue *vq)
 int
 vhost_user_iotlb_init(struct virtio_net *dev, struct vhost_virtqueue *vq)
 {
-	char pool_name[RTE_MEMPOOL_NAMESIZE];
+	unsigned int i;
 	int socket = 0;
 
 	if (vq->iotlb_pool) {
@@ -304,6 +325,7 @@ vhost_user_iotlb_init(struct virtio_net *dev, struct vhost_virtqueue *vq)
 		 * just drop all cached and pending entries.
 		 */
 		vhost_user_iotlb_flush_all(vq);
+		rte_free(vq->iotlb_pool);
 	}
 
 #ifdef RTE_LIBRTE_VHOST_NUMA
@@ -311,32 +333,32 @@ vhost_user_iotlb_init(struct virtio_net *dev, struct vhost_virtqueue *vq)
 		socket = 0;
 #endif
 
+	rte_spinlock_init(&vq->iotlb_free_lock);
 	rte_rwlock_init(&vq->iotlb_lock);
 	rte_rwlock_init(&vq->iotlb_pending_lock);
 
+	SLIST_INIT(&vq->iotlb_free_list);
 	TAILQ_INIT(&vq->iotlb_list);
 	TAILQ_INIT(&vq->iotlb_pending_list);
 
-	snprintf(pool_name, sizeof(pool_name), "iotlb_%u_%d_%d",
-			getpid(), dev->vid, vq->index);
-	VHOST_LOG_CONFIG(dev->ifname, DEBUG, "IOTLB cache name: %s\n", pool_name);
-
-	/* If already created, free it and recreate */
-	vq->iotlb_pool = rte_mempool_lookup(pool_name);
-	rte_mempool_free(vq->iotlb_pool);
-
-	vq->iotlb_pool = rte_mempool_create(pool_name,
-			IOTLB_CACHE_SIZE, sizeof(struct vhost_iotlb_entry), 0,
-			0, 0, NULL, NULL, NULL, socket,
-			RTE_MEMPOOL_F_NO_CACHE_ALIGN |
-			RTE_MEMPOOL_F_SP_PUT);
+	vq->iotlb_pool = rte_calloc_socket("iotlb", IOTLB_CACHE_SIZE,
+		sizeof(struct vhost_iotlb_entry), 0, socket);
 	if (!vq->iotlb_pool) {
-		VHOST_LOG_CONFIG(dev->ifname, ERR, "Failed to create IOTLB cache pool %s\n",
-			pool_name);
+		VHOST_LOG_CONFIG(dev->ifname, ERR,
+			"Failed to create IOTLB cache pool for vq %"PRIu32"\n",
+			vq->index);
 		return -1;
 	}
+	for (i = 0; i < IOTLB_CACHE_SIZE; i++)
+		vhost_user_iotlb_pool_put(vq, &vq->iotlb_pool[i]);
 
 	vq->iotlb_cache_nr = 0;
 
 	return 0;
 }
+
+void
+vhost_user_iotlb_destroy(struct vhost_virtqueue *vq)
+{
+	rte_free(vq->iotlb_pool);
+}
diff --git a/lib/vhost/iotlb.h b/lib/vhost/iotlb.h
index 738e31e7b9..e27ebebcf5 100644
--- a/lib/vhost/iotlb.h
+++ b/lib/vhost/iotlb.h
@@ -48,5 +48,6 @@ void vhost_user_iotlb_pending_remove(struct vhost_virtqueue *vq, uint64_t iova,
 						uint64_t size, uint8_t perm);
 void vhost_user_iotlb_flush_all(struct vhost_virtqueue *vq);
 int vhost_user_iotlb_init(struct virtio_net *dev, struct vhost_virtqueue *vq);
+void vhost_user_iotlb_destroy(struct vhost_virtqueue *vq);
 
 #endif /* _VHOST_IOTLB_H_ */
diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
index 1b17233652..aa671f47a3 100644
--- a/lib/vhost/vhost.c
+++ b/lib/vhost/vhost.c
@@ -394,7 +394,7 @@ free_vq(struct virtio_net *dev, struct vhost_virtqueue *vq)
 
 	vhost_free_async_mem(vq);
 	rte_free(vq->batch_copy_elems);
-	rte_mempool_free(vq->iotlb_pool);
+	vhost_user_iotlb_destroy(vq);
 	rte_free(vq->log_cache);
 	rte_free(vq);
 }
diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index c6260b54cc..782d916ae0 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -299,10 +299,12 @@ struct vhost_virtqueue {
 
 	rte_rwlock_t	iotlb_lock;
 	rte_rwlock_t	iotlb_pending_lock;
-	struct rte_mempool *iotlb_pool;
+	struct vhost_iotlb_entry *iotlb_pool;
 	TAILQ_HEAD(, vhost_iotlb_entry) iotlb_list;
 	TAILQ_HEAD(, vhost_iotlb_entry) iotlb_pending_list;
 	int				iotlb_cache_nr;
+	rte_spinlock_t	iotlb_free_lock;
+	SLIST_HEAD(, vhost_iotlb_entry) iotlb_free_list;
 
 	/* Used to notify the guest (trigger interrupt) */
 	int			callfd;
-- 
2.36.1