netdev - Re: [PATCH v2] tcp: splice as many packets as possible at once

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Date:	Tue, 20 Jan 2009 09:33:52 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	herbert@...dor.apana.org.au, w@....eu, zbr@...emap.net,
	dada1@...mosbay.com, ben@...s.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jens.axboe@...cle.com
Subject: Re: [PATCH v2] tcp: splice as many packets as possible at once

On Tue, Jan 20, 2009 at 08:37:26AM +0000, Jarek Poplawski wrote:
...
> Here is a tiny upgrade to save some memory by reusing a page for more
> chunks if possible, which I think could be considered, after the
> testing of the main patch is finished. (There could be also added an
> additional freeing of this cached page before socket destruction,
> maybe in tcp_splice_read(), if somebody finds good place.)

OOPS! I did it again... Here is better refcounting.

Jarek P.

--- (take 2)

 include/net/sock.h  |    4 ++++
 net/core/skbuff.c   |   32 ++++++++++++++++++++++++++------
 net/core/sock.c     |    2 ++
 net/ipv4/tcp_ipv4.c |    8 ++++++++
 4 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 5a3a151..4ded741 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -190,6 +190,8 @@ struct sock_common {
   *	@sk_user_data: RPC layer private data
   *	@sk_sndmsg_page: cached page for sendmsg
   *	@sk_sndmsg_off: cached offset for sendmsg
+  *	@sk_splice_page: cached page for splice
+  *	@sk_splice_off: cached offset for splice
   *	@sk_send_head: front of stuff to transmit
   *	@sk_security: used by security modules
   *	@sk_mark: generic packet mark
@@ -279,6 +281,8 @@ struct sock {
 	struct page		*sk_sndmsg_page;
 	struct sk_buff		*sk_send_head;
 	__u32			sk_sndmsg_off;
+	struct page		*sk_splice_page;
+	__u32			sk_splice_off;
 	int			sk_write_pending;
 #ifdef CONFIG_SECURITY
 	void			*sk_security;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 56272ac..02a1a6c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1334,13 +1334,33 @@ static void sock_spd_release(struct splice_pipe_desc *spd, unsigned int i)
 }
 
 static inline struct page *linear_to_page(struct page *page, unsigned int len,
-					  unsigned int offset)
+					  unsigned int *offset,
+					  struct sk_buff *skb)
 {
-	struct page *p = alloc_pages(GFP_KERNEL, 0);
+	struct sock *sk = skb->sk;
+	struct page *p = sk->sk_splice_page;
+	unsigned int off;
 
-	if (!p)
-		return NULL;
-	memcpy(page_address(p) + offset, page_address(page) + offset, len);
+	if (!p) {
+new_page:
+		p = sk->sk_splice_page = alloc_pages(sk->sk_allocation, 0);
+		if (!p)
+			return NULL;
+
+		off = sk->sk_splice_off = 0;
+		/* we hold one ref to this page until it's full or unneeded */
+	} else {
+		off = sk->sk_splice_off;
+		if (off + len > PAGE_SIZE) {
+			put_page(p);
+			goto new_page;
+		}
+	}
+
+	memcpy(page_address(p) + off, page_address(page) + *offset, len);
+	sk->sk_splice_off += len;
+	*offset = off;
+	get_page(p);
 
 	return p;
 }
@@ -1356,7 +1376,7 @@ static inline int spd_fill_page(struct splice_pipe_desc *spd, struct page *page,
 		return 1;
 
 	if (linear) {
-		page = linear_to_page(page, len, offset);
+		page = linear_to_page(page, len, &offset, skb);
 		if (!page)
 			return 1;
 	} else
diff --git a/net/core/sock.c b/net/core/sock.c
index f3a0d08..6b258a9 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1732,6 +1732,8 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 
 	sk->sk_sndmsg_page	=	NULL;
 	sk->sk_sndmsg_off	=	0;
+	sk->sk_splice_page	=	NULL;
+	sk->sk_splice_off	=	0;
 
 	sk->sk_peercred.pid 	=	0;
 	sk->sk_peercred.uid	=	-1;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 19d7b42..cf3d367 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1848,6 +1848,14 @@ void tcp_v4_destroy_sock(struct sock *sk)
 		sk->sk_sndmsg_page = NULL;
 	}
 
+	/*
+	 * If splice cached page exists, toss it.
+	 */
+	if (sk->sk_splice_page) {
+		__free_page(sk->sk_splice_page);
+		sk->sk_splice_page = NULL;
+	}
+
 	percpu_counter_dec(&tcp_sockets_allocated);
 }
 
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