target/linux/generic/patches-3.18/656-skb_reduce_truesize-helper.patch

   1 From 4593a806e31119c5bd3faa00c7210ad862d515af Mon Sep 17 00:00:00 2001
   2 From: Dave Taht <dave.taht@bufferbloat.net>
   3 Date: Mon, 31 Dec 2012 10:02:21 -0800
   4 Subject: [PATCH 3/7] skb_reduce_truesize: helper function for shrinking skbs
   5  whenever needed
   6
   7 On embedded devices in particular, large queues of small packets from the rx
   8 path with a large truesize can exist. Reducing their size can reduce
   9 memory pressure. skb_reduce_truesize is a helper function for doing this,
  10 when needed.
  11 ---
  12  include/linux/skbuff.h |   18 ++++++++++++++++++
  13  1 file changed, 18 insertions(+)
  14
  15 --- a/include/linux/skbuff.h
  16 +++ b/include/linux/skbuff.h
  17 @@ -2068,6 +2068,24 @@ static inline void pskb_trim_unique(stru
  18         BUG_ON(err);
  19  }
  20
  21 +/*
  22 + * Caller wants to reduce memory needs before queueing skb
  23 + * The (expensive) copy should not be be done in fast path.
  24 + */
  25 +static inline struct sk_buff *skb_reduce_truesize(struct sk_buff *skb)
  26 +{
  27 +       if (skb->truesize > 2 * SKB_TRUESIZE(skb->len)) {
  28 +               struct sk_buff *nskb;
  29 +               nskb = skb_copy_expand(skb, skb_headroom(skb), 0,
  30 +                       GFP_ATOMIC | __GFP_NOWARN);
  31 +               if (nskb) {
  32 +                       __kfree_skb(skb);
  33 +                       skb = nskb;
  34 +               }
  35 +       }
  36 +       return skb;
  37 +}
  38 +
  39  /**
  40   *     skb_orphan - orphan a buffer
  41   *     @skb: buffer to orphan