[RFC PATCH 12/35] libceph: Bypass the messenger-v1 Tx loop for databuf/iter data blobs

[David Howells <dhowells@xxxxxxxxxx>]

Don't use the messenger-v1 Tx loop for databuf/iter data blobs, which sends
page fragments individually, but rather pass the entire iterator to the
socket in one go.  This uses the loop inside of tcp_sendmsg() to do the
work and allows TCP to make better choices.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Viacheslav Dubeyko <slava@xxxxxxxxxxx>
cc: Alex Markuze <amarkuze@xxxxxxxxxx>
cc: Ilya Dryomov <idryomov@xxxxxxxxx>
cc: ceph-devel@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
 include/linux/ceph/messenger.h |  1 +
 net/ceph/messenger.c           |  1 +
 net/ceph/messenger_v1.c        | 76 ++++++++++++++++++++++++++++------
 3 files changed, 65 insertions(+), 13 deletions(-)

diff --git a/include/linux/ceph/messenger.h b/include/linux/ceph/messenger.h
index 864aad369c91..1b646d0dff39 100644
--- a/include/linux/ceph/messenger.h
+++ b/include/linux/ceph/messenger.h
@@ -255,6 +255,7 @@ struct ceph_msg_data_cursor {
 		};
 		struct {
 			struct iov_iter		iov_iter;
+			struct iov_iter		crc_iter;
 			unsigned int		lastlen;
 		};
 	};
diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
index 02439b38ec94..dc8082575e4f 100644
--- a/net/ceph/messenger.c
+++ b/net/ceph/messenger.c
@@ -975,6 +975,7 @@ static void ceph_msg_data_iter_cursor_init(struct ceph_msg_data_cursor *cursor,
 	struct ceph_msg_data *data = cursor->data;
 
 	cursor->iov_iter = data->iter;
+	cursor->crc_iter = data->iter;
 	cursor->lastlen = 0;
 	iov_iter_truncate(&cursor->iov_iter, length);
 	cursor->resid = iov_iter_count(&cursor->iov_iter);
diff --git a/net/ceph/messenger_v1.c b/net/ceph/messenger_v1.c
index 0cb61c76b9b8..d6464ac62b09 100644
--- a/net/ceph/messenger_v1.c
+++ b/net/ceph/messenger_v1.c
@@ -3,6 +3,7 @@
 
 #include <linux/bvec.h>
 #include <linux/crc32c.h>
+#include <linux/iov_iter.h>
 #include <linux/net.h>
 #include <linux/socket.h>
 #include <net/sock.h>
@@ -74,6 +75,21 @@ static int ceph_tcp_sendmsg(struct socket *sock, struct kvec *iov,
 	return r;
 }
 
+static int ceph_tcp_sock_sendmsg(struct socket *sock, struct iov_iter *iter,
+				 unsigned int flags)
+{
+	struct msghdr msg = {
+		.msg_iter  = *iter,
+		.msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL | flags,
+	};
+	int r;
+
+	r = sock_sendmsg(sock, &msg);
+	if (r == -EAGAIN)
+		r = 0;
+	return r;
+}
+
 /*
  * @more: MSG_MORE or 0.
  */
@@ -455,6 +471,24 @@ static int write_partial_kvec(struct ceph_connection *con)
 	return ret;  /* done! */
 }
 
+static size_t ceph_crc_from_iter(void *iter_from, size_t progress,
+				 size_t len, void *priv, void *priv2)
+{
+	u32 *crc = priv;
+
+	*crc = crc32c(*crc, iter_from, len);
+	return 0;
+}
+
+static void ceph_calc_crc(struct iov_iter *iter, size_t count, u32 *crc)
+{
+	size_t done;
+
+	done = iterate_and_advance_kernel(iter, count, crc, NULL,
+					  ceph_crc_from_iter);
+	WARN_ON(done != count);
+}
+
 /*
  * Write as much message data payload as we can.  If we finish, queue
  * up the footer.
@@ -467,7 +501,7 @@ static int write_partial_message_data(struct ceph_connection *con)
 	struct ceph_msg *msg = con->out_msg;
 	struct ceph_msg_data_cursor *cursor = &msg->cursor;
 	bool do_datacrc = !ceph_test_opt(from_msgr(con->msgr), NOCRC);
-	u32 crc;
+	u32 crc = 0;
 
 	dout("%s %p msg %p\n", __func__, con, msg);
 
@@ -484,9 +518,6 @@ static int write_partial_message_data(struct ceph_connection *con)
 	 */
 	crc = do_datacrc ? le32_to_cpu(msg->footer.data_crc) : 0;
 	while (cursor->total_resid) {
-		struct page *page;
-		size_t page_offset;
-		size_t length;
 		int ret;
 
 		if (!cursor->resid) {
@@ -494,17 +525,36 @@ static int write_partial_message_data(struct ceph_connection *con)
 			continue;
 		}
 
-		page = ceph_msg_data_next(cursor, &page_offset, &length);
-		ret = ceph_tcp_sendpage(con->sock, page, page_offset, length,
-					MSG_MORE);
-		if (ret <= 0) {
-			if (do_datacrc)
-				msg->footer.data_crc = cpu_to_le32(crc);
+		if (cursor->data->type == CEPH_MSG_DATA_DATABUF ||
+		    cursor->data->type == CEPH_MSG_DATA_ITER) {
+			ret = ceph_tcp_sock_sendmsg(con->sock, &cursor->iov_iter,
+						    MSG_MORE);
+			if (ret <= 0) {
+				if (do_datacrc)
+					msg->footer.data_crc = cpu_to_le32(crc);
 
-			return ret;
+				return ret;
+			}
+			if (do_datacrc && cursor->need_crc)
+				ceph_calc_crc(&cursor->crc_iter, ret, &crc);
+		} else {
+			struct page *page;
+			size_t page_offset;
+			size_t length;
+
+			page = ceph_msg_data_next(cursor, &page_offset, &length);
+			ret = ceph_tcp_sendpage(con->sock, page, page_offset,
+						length, MSG_MORE);
+			if (ret <= 0) {
+				if (do_datacrc)
+					msg->footer.data_crc = cpu_to_le32(crc);
+
+				return ret;
+			}
+			if (do_datacrc && cursor->need_crc)
+				crc = ceph_crc32c_page(crc, page, page_offset,
+						       length);
 		}
-		if (do_datacrc && cursor->need_crc)
-			crc = ceph_crc32c_page(crc, page, page_offset, length);
 		ceph_msg_data_advance(cursor, (size_t)ret);
 	}