Commit 826ff799 authored by Eric Dumazet's avatar Eric Dumazet Committed by Greg Kroah-Hartman

inet: frags: get rid of ipfrag_skb_cb/FRAG_CB

commit bf66337140c64c27fa37222b7abca7e49d63fb57 upstream.

ip_defrag uses skb->cb[] to store the fragment offset, and unfortunately
this integer is currently in a different cache line than skb->next,
meaning that we use two cache lines per skb when finding the insertion point.

By aliasing skb->ip_defrag_offset and skb->dev, we pack all the fields
in a single cache line and save precious memory bandwidth.

Note that after the fast path added by Changli Gao in commit
d6bebca9 ("fragment: add fast path for in-order fragments")
this change wont help the fast path, since we still need
to access prev->len (2nd cache line), but will show great
benefits when slow path is entered, since we perform
a linear scan of a potentially long list.

Also, note that this potential long list is an attack vector,
we might consider also using an rb-tree there eventually.
Signed-off-by: 's avatarEric Dumazet <>
Signed-off-by: 's avatarDavid S. Miller <>
Signed-off-by: 's avatarBen Hutchings <>
Signed-off-by: 's avatarGreg Kroah-Hartman <>
parent 29ff723c
......@@ -558,6 +558,11 @@ struct sk_buff {
struct rb_node rbnode; /* used in netem & tcp stack */
union {
int ip_defrag_offset;
struct sock *sk;
struct net_device *dev;
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