[PATCH net-next v2 3/3] net: devmem: batch net_iov allocations into the page_pool cache

[Stanislav Fomichev <sdf.kernel@gmail.com>]

Rename net_devmem_alloc_dmabuf() into net_devmem_alloc_dmabuf_bulk() and
make it refill page pool with up to PP_ALLOC_CACHE_REFILL NIOVs,
similar to io_pp_zc_alloc_netmems(). That should amortize recently
introduced freelist_lock.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
---
 net/core/devmem.c | 59 +++++++++++++++++++++++++++++------------------
 net/core/devmem.h |  8 -------
 2 files changed, 37 insertions(+), 30 deletions(-)

diff --git a/net/core/devmem.c b/net/core/devmem.c
index 7949f8425bcd..a0dcc896dd12 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -58,25 +58,25 @@ void __net_devmem_dmabuf_binding_free(struct work_struct *wq)
 	kfree(binding);
 }
 
-struct net_iov *
-net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding)
+static unsigned int
+net_devmem_alloc_dmabuf_bulk(struct net_devmem_dmabuf_binding *binding,
+			     netmem_ref *netmems, unsigned int count)
 {
-	struct net_iov *niov;
+	unsigned int i;
+
 	spin_lock_bh(&binding->freelist_lock);
-	if (unlikely(!binding->free_count)) {
-		spin_unlock_bh(&binding->freelist_lock);
-		return NULL;
+
+	count = min_t(size_t, count, binding->free_count);
+	for (i = 0; i < count; i++) {
+		struct net_iov *niov = binding->freelist[--binding->free_count];
+
+		binding->freelist[binding->free_count] = NULL;
+		netmems[i] = net_iov_to_netmem(niov);
 	}
 
-	niov = binding->freelist[--binding->free_count];
-	binding->freelist[binding->free_count] = NULL;
 	spin_unlock_bh(&binding->freelist_lock);
 
-	niov->desc.pp_magic = 0;
-	niov->desc.pp = NULL;
-	atomic_long_set(&niov->desc.pp_ref_count, 0);
-
-	return niov;
+	return count;
 }
 
 void net_devmem_free_dmabuf(struct net_iov *niov)
@@ -434,20 +434,35 @@ int mp_dmabuf_devmem_init(struct page_pool *pool)
 netmem_ref mp_dmabuf_devmem_alloc_netmems(struct page_pool *pool, gfp_t gfp)
 {
 	struct net_devmem_dmabuf_binding *binding = pool->mp_priv;
-	struct net_iov *niov;
-	netmem_ref netmem;
+	netmem_ref *netmems = pool->alloc.cache;
+	unsigned int allocated, i;
+
+	if (WARN_ON_ONCE(pool->alloc.count))
+		return 0;
 
-	niov = net_devmem_alloc_dmabuf(binding);
-	if (!niov)
+	allocated = net_devmem_alloc_dmabuf_bulk(binding, netmems,
+						 PP_ALLOC_CACHE_REFILL);
+	if (unlikely(!allocated))
 		return 0;
 
-	netmem = net_iov_to_netmem(niov);
+	for (i = 0; i < allocated; i++) {
+		struct net_iov *niov = netmem_to_net_iov(netmems[i]);
 
-	page_pool_set_pp_info(pool, netmem);
+		niov->desc.pp_magic = 0;
+		niov->desc.pp = NULL;
+		atomic_long_set(&niov->desc.pp_ref_count, 0);
+
+		page_pool_set_pp_info(pool, netmems[i]);
+
+		pool->pages_state_hold_cnt++;
+		trace_page_pool_state_hold(pool, netmems[i],
+					   pool->pages_state_hold_cnt);
+	}
 
-	pool->pages_state_hold_cnt++;
-	trace_page_pool_state_hold(pool, netmem, pool->pages_state_hold_cnt);
-	return netmem;
+	/* Return the last one, the rest stay in the page_pool cache. */
+	allocated--;
+	pool->alloc.count = allocated;
+	return netmems[allocated];
 }
 
 void mp_dmabuf_devmem_destroy(struct page_pool *pool)
diff --git a/net/core/devmem.h b/net/core/devmem.h
index 20a3eb90ea7f..7195769b8bd1 100644
--- a/net/core/devmem.h
+++ b/net/core/devmem.h
@@ -133,8 +133,6 @@ net_devmem_dmabuf_binding_put(struct net_devmem_dmabuf_binding *binding)
 void net_devmem_get_net_iov(struct net_iov *niov);
 void net_devmem_put_net_iov(struct net_iov *niov);
 
-struct net_iov *
-net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding);
 void net_devmem_free_dmabuf(struct net_iov *ppiov);
 
 
@@ -191,12 +189,6 @@ net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx,
 	return -EOPNOTSUPP;
 }
 
-static inline struct net_iov *
-net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding)
-{
-	return NULL;
-}
-
 static inline void net_devmem_free_dmabuf(struct net_iov *ppiov)
 {
 }
-- 
2.53.0-Meta