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net: don't reallocate skb->head unless the current one hasn't the needed extra size or is shared

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skb head being allocated by kmalloc(), it might be larger than what
actually requested because of discrete kmem caches sizes. Before
reallocating a new skb head, check if the current one has the needed
extra size.

Do this check only if skb head is not shared.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Changli Gao 2010-11-29 22:48:46 +00:00 committed by David S. Miller
parent 289700dbc4
commit ca44ac3861
1 changed files with 23 additions and 11 deletions
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34
net/core/skbuff.c
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@ -778,6 +778,28 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
size = SKB_DATA_ALIGN(size);
/* Check if we can avoid taking references on fragments if we own
* the last reference on skb->head. (see skb_release_data())
*/
if (!skb->cloned)
fastpath = true;
else {
int delta = skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1;
fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
}
if (fastpath &&
size + sizeof(struct skb_shared_info) <= ksize(skb->head)) {
memmove(skb->head + size, skb_shinfo(skb),
offsetof(struct skb_shared_info,
frags[skb_shinfo(skb)->nr_frags]));
memmove(skb->head + nhead, skb->head,
skb_tail_pointer(skb) - skb->head);
off = nhead;
goto adjust_others;
}
data = kmalloc(size + sizeof(struct skb_shared_info), gfp_mask);
if (!data)
goto nodata;
@ -791,17 +813,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
skb_shinfo(skb),
offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));
/* Check if we can avoid taking references on fragments if we own
* the last reference on skb->head. (see skb_release_data())
*/
if (!skb->cloned)
fastpath = true;
else {
int delta = skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1;
fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
}
if (fastpath) {
kfree(skb->head);
} else {
@ -816,6 +827,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
off = (data + nhead) - skb->head;
skb->head = data;
adjust_others:
skb->data += off;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
skb->end = size;