Xen devel - Apr 2012 - [PATCH 07/10] net: only allow paged fragments with the same destructor to be coalesced.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: "Pekka Savola (ipv6)" <pekkas@netcore.fi>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Cc: netdev@vger.kernel.org
---
 include/linux/skbuff.h |    7 +++++--
 net/core/skbuff.c      |    1 +
 net/ipv4/ip_output.c   |    2 +-
 net/ipv4/tcp.c         |    4 ++--
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 6ac283e..8593ac2 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2014,13 +2014,16 @@ static inline int skb_add_data(struct sk_buff *skb,
 }
 
 static inline int skb_can_coalesce(struct sk_buff *skb, int i,
-				   const struct page *page, int off)
+				   const struct page *page,
+				   const struct skb_frag_destructor *destroy,
+				   int off)
 {
 	if (i) {
 		const struct skb_frag_struct *frag = &skb_shinfo(skb)->frags[i - 1];
 
 		return page == skb_frag_page(frag) &&
-		       off == frag->page_offset + skb_frag_size(frag);
+		       off == frag->page_offset + skb_frag_size(frag) &&
+		       frag->page.destructor == destroy;
 	}
 	return 0;
 }
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 9ec88ce..e63a4a6 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2323,6 +2323,7 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb,
int shiftlen)
 	 */
 	if (!to ||
 	    !skb_can_coalesce(tgt, to, skb_frag_page(fragfrom),
+			      fragfrom->page.destructor,
 			      fragfrom->page_offset)) {
 		merge = -1;
 	} else {
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index ff302bd..9e4eca6 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1243,7 +1243,7 @@ ssize_t	ip_append_page(struct sock *sk, struct flowi4
*fl4, struct page *page,
 		i = skb_shinfo(skb)->nr_frags;
 		if (len > size)
 			len = size;
-		if (skb_can_coalesce(skb, i, page, offset)) {
+		if (skb_can_coalesce(skb, i, page, NULL, offset)) {
 			skb_frag_size_add(&skb_shinfo(skb)->frags[i-1], len);
 		} else if (i < MAX_SKB_FRAGS) {
 			get_page(page);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index cfd7edd..b1612e9 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -804,7 +804,7 @@ new_segment:
 			copy = size;
 
 		i = skb_shinfo(skb)->nr_frags;
-		can_coalesce = skb_can_coalesce(skb, i, page, offset);
+		can_coalesce = skb_can_coalesce(skb, i, page, NULL, offset);
 		if (!can_coalesce && i >= MAX_SKB_FRAGS) {
 			tcp_mark_push(tp, skb);
 			goto new_segment;
@@ -1013,7 +1013,7 @@ new_segment:
 
 				off = sk->sk_sndmsg_off;
 
-				if (skb_can_coalesce(skb, i, page, off) &&
+				if (skb_can_coalesce(skb, i, page, NULL, off) &&
 				    off != PAGE_SIZE) {
 					/* We can extend the last page
 					 * fragment. */
-- 
1.7.2.5


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Shouldn''t this be folded into the previous change ''net: add
support for
per-paged-fragment destructors''?  Maybe it doesn''t matter
since nothing
is setting a non-NULL fragment destructor yet.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that''s the marketing
department''s job.
They asked us to note that Solarflare product names are trademarked.

On Tue, 2012-04-10 at 21:11 +0100, Ben Hutchings wrote:
> Shouldn''t this be folded into the previous change ''net:
add support for
> per-paged-fragment destructors''?  Maybe it doesn''t matter
since nothing
> is setting a non-NULL fragment destructor yet.
I keep following exactly the same thought pattern and then ending up
leaving it due to indecision. I''ll squash it next time unless anyone
thinks it is worth keeping split out.

Ian.