From 4593a806e31119c5bd3faa00c7210ad862d515af Mon Sep 17 00:00:00 2001 From: Dave Taht <dave.taht@bufferbloat.net> Date: Mon, 31 Dec 2012 10:02:21 -0800 Subject: [PATCH 3/7] skb_reduce_truesize: helper function for shrinking skbs whenever needed On embedded devices in particular, large queues of small packets from the rx path with a large truesize can exist. Reducing their size can reduce memory pressure. skb_reduce_truesize is a helper function for doing this, when needed. --- include/linux/skbuff.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1772,6 +1772,24 @@ static inline void pskb_trim_unique(stru BUG_ON(err); } +/* + * Caller wants to reduce memory needs before queueing skb + * The (expensive) copy should not be be done in fast path. + */ +static inline struct sk_buff *skb_reduce_truesize(struct sk_buff *skb) +{ + if (skb->truesize > 2 * SKB_TRUESIZE(skb->len)) { + struct sk_buff *nskb; + nskb = skb_copy_expand(skb, skb_headroom(skb), 0, + GFP_ATOMIC | __GFP_NOWARN); + if (nskb) { + __kfree_skb(skb); + skb = nskb; + } + } + return skb; +} + /** * skb_orphan - orphan a buffer * @skb: buffer to orphan