• Eric Dumazet's avatar
    inet: frags: get rid of ipfrag_skb_cb/FRAG_CB · bf663371
    Eric Dumazet authored
    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: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    bf663371
ip_fragment.c 20.7 KB