kernel: add patches by Dave Täht to reduce buffer size in longer queues to reduce memory pressure

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36301 3c298f89-4303-0410-b956-a3cf2f4a3e73

1 files changed, 41 insertions, 0 deletions

diff --git a/target/linux/generic/patches-3.8/656-skb_reduce_truesize-helper.patch b/target/linux/generic/patches-3.8/656-skb_reduce_truesize-helper.patch
new file mode 100644
index 000000000..e538eade8
--- /dev/null
+++ b/target/linux/generic/patches-3.8/656-skb_reduce_truesize-helper.patch
@@ -0,0 +1,41 @@
+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