netdev - [bpf-next PATCH 03/16] net: do_tcp_sendpages flag to avoid SKBTX_SHARED

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Message-ID: <20180305195111.6612.44347.stgit@john-Precision-Tower-5810>
Date:   Mon, 05 Mar 2018 11:51:12 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     ast@...nel.org, daniel@...earbox.net
Cc:     netdev@...r.kernel.org, davejwatson@...com
Subject: [bpf-next PATCH 03/16] net: do_tcp_sendpages flag to avoid
 SKBTX_SHARED_FRAG

When calling do_tcp_sendpages() from in kernel and we know the data
has no references from user side we can omit SKBTX_SHARED_FRAG flag.
This patch adds an internal flag, NO_SKBTX_SHARED_FRAG that can be used
to omit setting SKBTX_SHARED_FRAG.

The flag is not exposed to userspace because the sendpage call from
the splice logic masks out all bits except MSG_MORE.

Signed-off-by: John Fastabend <john.fastabend@...il.com>
---
 include/linux/socket.h |    1 +
 net/ipv4/tcp.c         |    4 +++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 1ce1f76..60e0148 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -287,6 +287,7 @@ struct ucred {
 #define MSG_SENDPAGE_NOTLAST 0x20000 /* sendpage() internal : not the last page */
 #define MSG_BATCH	0x40000 /* sendmmsg(): more messages coming */
 #define MSG_EOF         MSG_FIN
+#define MSG_NO_SHARED_FRAGS 0x80000 /* sendpage() internal : page frags are not shared */
 
 #define MSG_ZEROCOPY	0x4000000	/* Use user data in kernel path */
 #define MSG_FASTOPEN	0x20000000	/* Send data in TCP SYN */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index a335397..ff8a8d3 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -994,7 +994,9 @@ ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
 			get_page(page);
 			skb_fill_page_desc(skb, i, page, offset, copy);
 		}
-		skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
+
+		if (!(flags & MSG_NO_SHARED_FRAGS))
+			skb_shinfo(skb)->tx_flags |= SKBTX_SHARED_FRAG;
 
 		skb->len += copy;
 		skb->data_len += copy;