[ 59/61] net: splice: avoid high order page splitting

Greg Kroah-Hartman
2013-02-12T20:36:29Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 82bda6195615891181115f579a480aa5001ce7e9 ]

splice() can handle pages of any order, but network code tries hard to
split them in PAGE_SIZE units. Not quite successfully anyway, as
__splice_segment() assumed poff < PAGE_SIZE. This is true for
the skb->data part, not necessarily for the fragments.

This patch removes this logic to give the pages as they are in the skb.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/skbuff.c | 38 +++++++++-----------------------------
1 file changed, 9 insertions(+), 29 deletions(-)

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1677,20 +1677,6 @@ static bool spd_fill_page(struct splice_
return false;
}

-static inline void __segment_seek(struct page **page, unsigned int *poff,
- unsigned int *plen, unsigned int off)
-{
- unsigned long n;
-
- *poff += off;
- n = *poff / PAGE_SIZE;
- if (n)
- *page = nth_page(*page, n);
-
- *poff = *poff % PAGE_SIZE;
- *plen -= off;
-}
-
static bool __splice_segment(struct page *page, unsigned int poff,
unsigned int plen, unsigned int *off,
unsigned int *len, struct sk_buff *skb,
@@ -1698,6 +1684,8 @@ static bool __splice_segment(struct page
struct sock *sk,
struct pipe_inode_info *pipe)
{
+ unsigned int flen;
+
if (!*len)
return true;

@@ -1708,24 +1696,16 @@ static bool __splice_segment(struct page
}

/* ignore any bits we already processed */
- if (*off) {
- __segment_seek(&page, &poff, &plen, *off);
- *off = 0;
- }
-
- do {
- unsigned int flen = min(*len, plen);
+ poff += *off;
+ plen -= *off;
+ *off = 0;

- /* the linear region may spread across several pages */
- flen = min_t(unsigned int, flen, PAGE_SIZE - poff);
+ flen = min(*len, plen);

- if (spd_fill_page(spd, pipe, page, &flen, poff, skb, linear, sk))
- return true;
-
- __segment_seek(&page, &poff, &plen, flen);
- *len -= flen;
+ if (spd_fill_page(spd, pipe, page, &flen, poff, skb, linear, sk))
+ return true;

- } while (*len && plen);
+ *len -= flen;

return false;
}