lkml.org 
[lkml]   [2019]   [Feb]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.4 20/34] inet: frags: get rid of ipfrag_skb_cb/FRAG_CB
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eric Dumazet <edumazet@google.com>

    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
    d6bebca92c66 ("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: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    include/linux/skbuff.h | 5 +++++
    1 file changed, 5 insertions(+)

    --- a/include/linux/skbuff.h
    +++ b/include/linux/skbuff.h
    @@ -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;


    \
     
     \ /
      Last update: 2019-02-07 12:45    [W:4.691 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site