fs: dlm: rework receive handling

This patch reworks the current receive handling of dlm. As I tried to
change the send handling to fix reorder issues I took a look into the
receive handling and simplified it, it works as the following:

Each connection has a preallocated receive buffer with a minimum length of
4096. On receive, the upper layer protocol will process all dlm message
until there is not enough data anymore. If there exists "leftover" data at
the end of the receive buffer because the dlm message wasn't fully received
it will be copied to the begin of the preallocated receive buffer. Next
receive more data will be appended to the previous "leftover" data and
processing will begin again.

This will remove a lot of code of the current mechanism. Inside the
processing functionality we will ensure with a memmove() that the dlm
message should be memory aligned. To have a dlm message always started
at the beginning of the buffer will reduce some amount of memmove()
calls because src and dest pointers are the same.

The cluster attribute "buffer_size" becomes a new meaning, it's now the
size of application layer receive buffer size. If this is changed during
runtime the receive buffer will be reallocated. It's important that the
receive buffer size has at minimum the size of the maximum possible dlm
message size otherwise the received message cannot be placed inside
the receive buffer size.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

1 files changed, 85 insertions, 94 deletions

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index 96f84541867c4..b7b7360be609e 100644
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -65,40 +65,6 @@
 #define MAX_SEND_MSG_COUNT 25
 #define DLM_SHUTDOWN_WAIT_TIMEOUT msecs_to_jiffies(10000)
 
-struct cbuf {
-	unsigned int base;
-	unsigned int len;
-	unsigned int mask;
-};
-
-static void cbuf_add(struct cbuf *cb, int n)
-{
-	cb->len += n;
-}
-
-static int cbuf_data(struct cbuf *cb)
-{
-	return ((cb->base + cb->len) & cb->mask);
-}
-
-static void cbuf_init(struct cbuf *cb, int size)
-{
-	cb->base = cb->len = 0;
-	cb->mask = size-1;
-}
-
-static void cbuf_eat(struct cbuf *cb, int n)
-{
-	cb->len  -= n;
-	cb->base += n;
-	cb->base &= cb->mask;
-}
-
-static bool cbuf_empty(struct cbuf *cb)
-{
-	return cb->len == 0;
-}
-
 struct connection {
 	struct socket *sock;	/* NULL if not connected */
 	uint32_t nodeid;	/* So we know who we are in the list */
@@ -117,8 +83,6 @@ struct connection {
 	int (*rx_action) (struct connection *);	/* What to do when active */
 	void (*connect_action) (struct connection *);	/* What to do to connect */
 	void (*shutdown_action)(struct connection *con); /* What to do to shutdown */
-	struct page *rx_page;
-	struct cbuf cb;
 	int retries;
 #define MAX_CONNECT_RETRIES 3
 	struct hlist_node list;
@@ -126,6 +90,9 @@ struct connection {
 	struct work_struct rwork; /* Receive workqueue */
 	struct work_struct swork; /* Send workqueue */
 	wait_queue_head_t shutdown_wait; /* wait for graceful shutdown */
+	unsigned char *rx_buf;
+	int rx_buflen;
+	int rx_leftover;
 	struct rcu_head rcu;
 };
 #define sock2con(x) ((struct connection *)(x)->sk_user_data)
@@ -219,6 +186,13 @@ static struct connection *nodeid2con(int nodeid, gfp_t alloc)
 	if (!con)
 		return NULL;
 
+	con->rx_buflen = dlm_config.ci_buffer_size;
+	con->rx_buf = kmalloc(con->rx_buflen, GFP_NOFS);
+	if (!con->rx_buf) {
+		kfree(con);
+		return NULL;
+	}
+
 	con->nodeid = nodeid;
 	mutex_init(&con->sock_mutex);
 	INIT_LIST_HEAD(&con->writequeue);
@@ -613,11 +587,8 @@ static void close_connection(struct connection *con, bool and_other,
 		/* Will only re-enter once. */
 		close_connection(con->othercon, false, true, true);
 	}
-	if (con->rx_page) {
-		__free_page(con->rx_page);
-		con->rx_page = NULL;
-	}
 
+	con->rx_leftover = 0;
 	con->retries = 0;
 	mutex_unlock(&con->sock_mutex);
 	clear_bit(CF_CLOSING, &con->flags);
@@ -671,16 +642,33 @@ static void dlm_tcp_shutdown(struct connection *con)
 	shutdown_connection(con);
 }
 
+static int con_realloc_receive_buf(struct connection *con, int newlen)
+{
+	unsigned char *newbuf;
+
+	newbuf = kmalloc(newlen, GFP_NOFS);
+	if (!newbuf)
+		return -ENOMEM;
+
+	/* copy any leftover from last receive */
+	if (con->rx_leftover)
+		memmove(newbuf, con->rx_buf, con->rx_leftover);
+
+	/* swap to new buffer space */
+	kfree(con->rx_buf);
+	con->rx_buflen = newlen;
+	con->rx_buf = newbuf;
+
+	return 0;
+}
+
 /* Data received from remote end */
 static int receive_from_sock(struct connection *con)
 {
-	int ret = 0;
-	struct msghdr msg = {};
-	struct kvec iov[2];
-	unsigned len;
-	int r;
 	int call_again_soon = 0;
-	int nvec;
+	struct msghdr msg;
+	struct kvec iov;
+	int ret, buflen;
 
 	mutex_lock(&con->sock_mutex);
 
@@ -688,71 +676,55 @@ static int receive_from_sock(struct connection *con)
 		ret = -EAGAIN;
 		goto out_close;
 	}
+
 	if (con->nodeid == 0) {
 		ret = -EINVAL;
 		goto out_close;
 	}
 
-	if (con->rx_page == NULL) {
-		/*
-		 * This doesn't need to be atomic, but I think it should
-		 * improve performance if it is.
-		 */
-		con->rx_page = alloc_page(GFP_ATOMIC);
-		if (con->rx_page == NULL)
+	/* realloc if we get new buffer size to read out */
+	buflen = dlm_config.ci_buffer_size;
+	if (con->rx_buflen != buflen && con->rx_leftover <= buflen) {
+		ret = con_realloc_receive_buf(con, buflen);
+		if (ret < 0)
 			goto out_resched;
-		cbuf_init(&con->cb, PAGE_SIZE);
 	}
 
-	/*
-	 * iov[0] is the bit of the circular buffer between the current end
-	 * point (cb.base + cb.len) and the end of the buffer.
+	/* calculate new buffer parameter regarding last receive and
+	 * possible leftover bytes
 	 */
-	iov[0].iov_len = con->cb.base - cbuf_data(&con->cb);
-	iov[0].iov_base = page_address(con->rx_page) + cbuf_data(&con->cb);
-	iov[1].iov_len = 0;
-	nvec = 1;
+	iov.iov_base = con->rx_buf + con->rx_leftover;
+	iov.iov_len = con->rx_buflen - con->rx_leftover;
 
-	/*
-	 * iov[1] is the bit of the circular buffer between the start of the
-	 * buffer and the start of the currently used section (cb.base)
-	 */
-	if (cbuf_data(&con->cb) >= con->cb.base) {
-		iov[0].iov_len = PAGE_SIZE - cbuf_data(&con->cb);
-		iov[1].iov_len = con->cb.base;
-		iov[1].iov_base = page_address(con->rx_page);
-		nvec = 2;
-	}
-	len = iov[0].iov_len + iov[1].iov_len;
-	iov_iter_kvec(&msg.msg_iter, READ, iov, nvec, len);
-
-	r = ret = sock_recvmsg(con->sock, &msg, MSG_DONTWAIT | MSG_NOSIGNAL);
+	memset(&msg, 0, sizeof(msg));
+	msg.msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL;
+	ret = kernel_recvmsg(con->sock, &msg, &iov, 1, iov.iov_len,
+			     msg.msg_flags);
 	if (ret <= 0)
 		goto out_close;
-	else if (ret == len)
+	else if (ret == iov.iov_len)
 		call_again_soon = 1;
 
-	cbuf_add(&con->cb, ret);
-	ret = dlm_process_incoming_buffer(con->nodeid,
-					  page_address(con->rx_page),
-					  con->cb.base, con->cb.len,
-					  PAGE_SIZE);
-	if (ret < 0) {
-		log_print("lowcomms err %d: addr=%p, base=%u, len=%u, read=%d",
-			  ret, page_address(con->rx_page), con->cb.base,
-			  con->cb.len, r);
-		cbuf_eat(&con->cb, r);
-	} else {
-		cbuf_eat(&con->cb, ret);
-	}
+	/* new buflen according readed bytes and leftover from last receive */
+	buflen = ret + con->rx_leftover;
+	ret = dlm_process_incoming_buffer(con->nodeid, con->rx_buf, buflen);
+	if (ret < 0)
+		goto out_close;
 
-	if (cbuf_empty(&con->cb) && !call_again_soon) {
-		__free_page(con->rx_page);
-		con->rx_page = NULL;
+	/* calculate leftover bytes from process and put it into begin of
+	 * the receive buffer, so next receive we have the full message
+	 * at the start address of the receive buffer.
+	 */
+	con->rx_leftover = buflen - ret;
+	if (con->rx_leftover) {
+		memmove(con->rx_buf, con->rx_buf + ret,
+			con->rx_leftover);
+		call_again_soon = true;
 	}
 
 	if (call_again_soon)
 		goto out_resched;
+
 	mutex_unlock(&con->sock_mutex);
 	return 0;
 
@@ -854,6 +826,17 @@ static int accept_from_sock(struct connection *con)
 				result = -ENOMEM;
 				goto accept_err;
 			}
+
+			othercon->rx_buflen = dlm_config.ci_buffer_size;
+			othercon->rx_buf = kmalloc(othercon->rx_buflen, GFP_NOFS);
+			if (!othercon->rx_buf) {
+				mutex_unlock(&newcon->sock_mutex);
+				kfree(othercon);
+				log_print("failed to allocate incoming socket receive buffer");
+				result = -ENOMEM;
+				goto accept_err;
+			}
+
 			othercon->nodeid = nodeid;
 			othercon->rx_action = receive_from_sock;
 			mutex_init(&othercon->sock_mutex);
@@ -1603,6 +1586,14 @@ static void shutdown_conn(struct connection *con)
 		con->shutdown_action(con);
 }
 
+static void connection_release(struct rcu_head *rcu)
+{
+	struct connection *con = container_of(rcu, struct connection, rcu);
+
+	kfree(con->rx_buf);
+	kfree(con);
+}
+
 static void free_conn(struct connection *con)
 {
 	close_connection(con, true, true, true);
@@ -1611,10 +1602,10 @@ static void free_conn(struct connection *con)
 	spin_unlock(&connections_lock);
 	if (con->othercon) {
 		clean_one_writequeue(con->othercon);
-		kfree_rcu(con->othercon, rcu);
+		call_rcu(&con->othercon->rcu, connection_release);
 	}
 	clean_one_writequeue(con);
-	kfree_rcu(con, rcu);
+	call_rcu(&con->rcu, connection_release);
 }
 
 static void work_flush(void)