Merge branch 'shrink-struct-ubuf_info'

Pavel Begunkov says:

====================
shrink struct ubuf_info

struct ubuf_info is large but not all fields are needed for all
cases. We have limited space in io_uring for it and large ubuf_info
prevents some struct embedding, even though we use only a subset
of the fields. It's also not very clean trying to use this typeless
extra space.

Shrink struct ubuf_info to only necessary fields used in generic paths,
namely ->callback, ->refcnt and ->flags, which take only 16 bytes. And
make MSG_ZEROCOPY and some other users to embed it into a larger struct
ubuf_info_msgzc mimicking the former ubuf_info.

Note, xen/vhost may also have some cleaning on top by creating
new structs containing ubuf_info but with proper types.
====================

Link: https://lore.kernel.org/r/cover.1663892211.git.asml.silence@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

4 files changed, 15 insertions, 13 deletions

diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 8174d7b2966c..1545cbee77a4 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -62,7 +62,7 @@ struct pending_tx_info {
 	 * ubuf_to_vif is a helper which finds the struct xenvif from a pointer
 	 * to this field.
 	 */
-	struct ubuf_info callback_struct;
+	struct ubuf_info_msgzc callback_struct;
 };
 
 #define XEN_NETIF_TX_RING_SIZE __CONST_RING_SIZE(xen_netif_tx, XEN_PAGE_SIZE)
diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index fb32ae82d9b0..e579ecd40b74 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -591,8 +591,8 @@ int xenvif_init_queue(struct xenvif_queue *queue)
 	}
 
 	for (i = 0; i < MAX_PENDING_REQS; i++) {
-		queue->pending_tx_info[i].callback_struct = (struct ubuf_info)
-			{ .callback = xenvif_zerocopy_callback,
+		queue->pending_tx_info[i].callback_struct = (struct ubuf_info_msgzc)
+			{ { .callback = xenvif_zerocopy_callback },
 			  { { .ctx = NULL,
 			      .desc = i } } };
 		queue->grant_tx_handle[i] = NETBACK_INVALID_HANDLE;
diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index a256695fc89e..3d2081bbbc86 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -133,7 +133,7 @@ static inline unsigned long idx_to_kaddr(struct xenvif_queue *queue,
 
 /* Find the containing VIF's structure from a pointer in pending_tx_info array
  */
-static inline struct xenvif_queue *ubuf_to_queue(const struct ubuf_info *ubuf)
+static inline struct xenvif_queue *ubuf_to_queue(const struct ubuf_info_msgzc *ubuf)
 {
 	u16 pending_idx = ubuf->desc;
 	struct pending_tx_info *temp =
@@ -1228,11 +1228,12 @@ static int xenvif_tx_submit(struct xenvif_queue *queue)
 	return work_done;
 }
 
-void xenvif_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *ubuf,
+void xenvif_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *ubuf_base,
 			      bool zerocopy_success)
 {
 	unsigned long flags;
 	pending_ring_idx_t index;
+	struct ubuf_info_msgzc *ubuf = uarg_to_msgzc(ubuf_base);
 	struct xenvif_queue *queue = ubuf_to_queue(ubuf);
 
 	/* This is the only place where we grab this lock, to protect callbacks
@@ -1241,7 +1242,7 @@ void xenvif_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *ubuf,
 	spin_lock_irqsave(&queue->callback_lock, flags);
 	do {
 		u16 pending_idx = ubuf->desc;
-		ubuf = (struct ubuf_info *) ubuf->ctx;
+		ubuf = (struct ubuf_info_msgzc *) ubuf->ctx;
 		BUG_ON(queue->dealloc_prod - queue->dealloc_cons >=
 			MAX_PENDING_REQS);
 		index = pending_index(queue->dealloc_prod);
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 68e4ecd1cc0e..d7a04d573988 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -118,7 +118,7 @@ struct vhost_net_virtqueue {
 	/* Number of XDP frames batched */
 	int batched_xdp;
 	/* an array of userspace buffers info */
-	struct ubuf_info *ubuf_info;
+	struct ubuf_info_msgzc *ubuf_info;
 	/* Reference counting for outstanding ubufs.
 	 * Protected by vq mutex. Writers must also take device mutex. */
 	struct vhost_net_ubuf_ref *ubufs;
@@ -382,8 +382,9 @@ static void vhost_zerocopy_signal_used(struct vhost_net *net,
 }
 
 static void vhost_zerocopy_callback(struct sk_buff *skb,
-				    struct ubuf_info *ubuf, bool success)
+				    struct ubuf_info *ubuf_base, bool success)
 {
+	struct ubuf_info_msgzc *ubuf = uarg_to_msgzc(ubuf_base);
 	struct vhost_net_ubuf_ref *ubufs = ubuf->ctx;
 	struct vhost_virtqueue *vq = ubufs->vq;
 	int cnt;
@@ -871,7 +872,7 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
 	size_t len, total_len = 0;
 	int err;
 	struct vhost_net_ubuf_ref *ubufs;
-	struct ubuf_info *ubuf;
+	struct ubuf_info_msgzc *ubuf;
 	bool zcopy_used;
 	int sent_pkts = 0;
 
@@ -907,14 +908,14 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
 			ubuf = nvq->ubuf_info + nvq->upend_idx;
 			vq->heads[nvq->upend_idx].id = cpu_to_vhost32(vq, head);
 			vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
-			ubuf->callback = vhost_zerocopy_callback;
 			ubuf->ctx = nvq->ubufs;
 			ubuf->desc = nvq->upend_idx;
-			ubuf->flags = SKBFL_ZEROCOPY_FRAG;
-			refcount_set(&ubuf->refcnt, 1);
+			ubuf->ubuf.callback = vhost_zerocopy_callback;
+			ubuf->ubuf.flags = SKBFL_ZEROCOPY_FRAG;
+			refcount_set(&ubuf->ubuf.refcnt, 1);
 			msg.msg_control = &ctl;
 			ctl.type = TUN_MSG_UBUF;
-			ctl.ptr = ubuf;
+			ctl.ptr = &ubuf->ubuf;
 			msg.msg_controllen = sizeof(ctl);
 			ubufs = nvq->ubufs;
 			atomic_inc(&ubufs->refcount);