[Devel] [PATCH hci-8.1 3/3] fs/fuse kio: refactor receive path in pcs_sockio_recv()

[Liu Kui]

The receive path consumes data one 4k page per kernel_recvmsg() call:
do_recv_one_seg() extracts a single page from the iov_iter, kmaps it
and receives into it, so a 1M message body costs up to 256 recvmsg
calls plus a page reference and kmap/kunmap per page.

Replace do_recv_one_seg() with do_sockio_recvmsg(), the receive twin
of do_sockio_sendmsg(): hand the whole remaining iov_iter to
sock_recvmsg() and let it drain everything available in one call.
The header read goes through the same helper too, replacing
do_sock_recv(), so the whole receive path now uses one recv primitive.

https://virtuozzo.atlassian.net/browse/VSTOR-142167

Signed-off-by: Liu Kui <kui.liu at virtuozzo.com>
---
 fs/fuse/kio/pcs/pcs_sock_io.c | 80 +++++++++++--------------------------------
 fs/fuse/kio/pcs/pcs_sock_io.h |  1 +
 2 files changed, 21 insertions(+), 60 deletions(-)

diff --git a/fs/fuse/kio/pcs/pcs_sock_io.c b/fs/fuse/kio/pcs/pcs_sock_io.c
index 828c8a98cabf..2da6d51c898b 100644
--- a/fs/fuse/kio/pcs/pcs_sock_io.c
+++ b/fs/fuse/kio/pcs/pcs_sock_io.c
@@ -139,69 +139,24 @@ static bool pcs_should_fail_sock_io(void)
 }
 #endif
 
-static int do_sock_recv(struct socket *sock, void *buf, size_t len)
+static int do_sockio_recvmsg(struct pcs_sockio *sio, struct iov_iter *it, size_t left)
 {
+	struct msghdr sockmsg = { .msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL };
+	int ret;
 
-	struct kvec iov = {buf, len};
-	struct msghdr msg = { .msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL };
-	struct pcs_sockio __maybe_unused *sio;
-	int ret = -EIO;
-
-	if (pcs_should_fail_sock_io())
-		goto out;
-
-	ret =  kernel_recvmsg(sock, &msg, &iov, 1, len, msg.msg_flags);
-out:
-
-#ifdef CONFIG_FUSE_KIO_DEBUG
-	rcu_read_lock();
-	sio = rcu_dereference_sk_user_data(sock->sk);
-	if (sio) {
-		TRACE("RET: "PEER_FMT" len:%ld ret:%d\n", PEER_ARGS(sio->netio.parent),
-		      len, ret);
-	}
-	rcu_read_unlock();
-#endif /* CONFIG_FUSE_KIO_DEBUG */
-
-	return ret;
-}
-
-static int do_recv_one_seg(struct socket *sock, struct iov_iter *it, size_t left)
-{
-	int ret = -EINVAL;
-	size_t size = min(iov_iter_single_seg_count(it), left);
-
-	if (unlikely(!size))
-		return 0;
-
-	if (iov_iter_is_kvec(it)) {
-		struct kvec kv;
-
-		iov_iter_get_kvec(it, &kv);
-		if (kv.iov_len > size)
-			kv.iov_len = size;
-
-		ret = do_sock_recv(sock, kv.iov_base, kv.iov_len);
-		if (ret > 0)
-			iov_iter_advance(it, ret);
+	if (unlikely(pcs_should_fail_sock_io()))
+		return -EIO;
 
-	} else if (iov_iter_is_bvec(it)) {
-		size_t offset;
-		ssize_t len;
-		struct page* page;
+	sockmsg.msg_iter = *it;
+	/* The iter may cover more than what is left of the message (trash msg) */
+	iov_iter_truncate(&sockmsg.msg_iter, left);
 
-		len = iov_iter_get_pages2(it, &page, size, 1, &offset);
-		BUG_ON(len <=0);
+	ret = sock_recvmsg(sio->socket, &sockmsg, sockmsg.msg_flags);
 
-		ret = do_sock_recv(sock, kmap(page) + offset, len);
-		if (ret <= 0)
-			iov_iter_revert(it, len);
-		else if (ret < len)
-			iov_iter_revert(it, len - ret);
+	DTRACE("sock(%px) len:%zu ret:%d\n", sio->socket, left, ret);
 
-		kunmap(page);
-		put_page(page);
-	}
+	if (ret > 0)
+		iov_iter_advance(it, ret);
 
 	return ret;
 }
@@ -232,8 +187,13 @@ static void pcs_sockio_recv(struct pcs_sockio *sio)
 			sio->read_offset = 0;
 			n = 0;
 
-			if (copy)
-				n = do_sock_recv(sio->socket, (char *)sio_inline_buffer(sio) + sio->hdr_ptr, copy);
+			if (copy) {
+				sio->hdr_kv.iov_base = (char *)sio_inline_buffer(sio) + sio->hdr_ptr;
+				sio->hdr_kv.iov_len = copy;
+				iov_iter_kvec(it, READ, &sio->hdr_kv, 1, copy);
+
+				n = do_sockio_recvmsg(sio, it, copy);
+			}
 
 			if (n > 0 || n == copy /* recv return 0 when copy is 0 */) {
 				sio->hdr_ptr += n;
@@ -279,7 +239,7 @@ static void pcs_sockio_recv(struct pcs_sockio *sio)
 				if (msg != PCS_TRASH_MSG)
 					BUG_ON(iov_iter_count(it) > msg_size - sio->read_offset);
 
-				n = do_recv_one_seg(sio->socket, it, (size_t)(msg_size - sio->read_offset));
+				n = do_sockio_recvmsg(sio, it, (size_t)(msg_size - sio->read_offset));
 				if (n > 0) {
 					sio->read_offset += n;
 				} else {
diff --git a/fs/fuse/kio/pcs/pcs_sock_io.h b/fs/fuse/kio/pcs/pcs_sock_io.h
index d894aebdca7f..01c99f73dc9d 100644
--- a/fs/fuse/kio/pcs/pcs_sock_io.h
+++ b/fs/fuse/kio/pcs/pcs_sock_io.h
@@ -151,6 +151,7 @@ struct pcs_sockio
 	u32			current_msg_size;
 	int			read_offset;
 	int			write_offset;
+	struct kvec		hdr_kv;		/* backs read_iter for header reads */
 	struct iov_iter		read_iter;
 	struct iov_iter		write_iter;
 	struct mutex		mutex;

-- 
Git-155)