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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
@@ -1893,6 +1893,24 @@ 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
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