[PATCH] net: allow pskb_expand_head() to get maximum tailroom

Eric Dumazet
2012-04-11T06:08:45Z

Marc Merlin reported many order-1 allocations failures in TX path on its
wireless setup, that dont make any sense with MTU=1500 network, and non
SG capable hardware.

Turns out part of the problem comes from pskb_expand_head() not using
ksize() to get exact head size given by kmalloc(). Doing the same thing
than __alloc_skb() allows more tailroom in skb and can prevent future
reallocations.

As a bonus, struct skb_shared_info becomes cache line aligned.

Reported-by: Marc MERLIN <marc@merlins.org>
Tested-by: Marc MERLIN <marc@merlins.org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
net/core/skbuff.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index baf8d28..e598400 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -952,9 +952,11 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
goto adjust_others;
}

- data = kmalloc(size + sizeof(struct skb_shared_info), gfp_mask);
+ data = kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
+ gfp_mask);
if (!data)
goto nodata;
+ size = SKB_WITH_OVERHEAD(ksize(data));

/* Copy only real data... and, alas, header. This should be
* optimized for the cases when header is void.