Commit c73c3d9c authored May 02, 2012 by Alexander Duyck Committed by David S. Miller May 03, 2012

tcp: Fix truesize accounting in tcp_try_coalesce



This patch addresses several issues in the way we were tracking the
truesize in tcp_try_coalesce.

First it was using ksize which prevents us from having a 0 sized head frag
and getting a usable result.  To resolve that this patch uses the end
pointer which is set based off either ksize, or the frag_size supplied in
build_skb.  This allows us to compute the original truesize of the entire
buffer and remove that value leaving us with just what was added as pages.

The second issue was the use of skb->len if there is a mergeable head frag.
We should only need to remove the size of an data aligned sk_buff from our
current skb->truesize to compute the delta for a buffer with a reused head.
By using skb->len the value of truesize was being artificially reduced
which means that head frags could use more memory than buffers using
standard allocations.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 8c1ae10d

net/ipv4/tcp_input.c

+4 −6

Original line number	Diff line number	Diff line
		@@ -4565,12 +4565,10 @@ merge:
		if (skb_headlen(from) == 0 &&
		(skb_shinfo(to)->nr_frags +
		skb_shinfo(from)->nr_frags <= MAX_SKB_FRAGS)) {
		WARN_ON_ONCE(from->head_frag);
		delta = from->truesize - ksize(from->head) -
		SKB_DATA_ALIGN(sizeof(struct sk_buff));

		WARN_ON_ONCE(delta < len);
		delta = from->truesize -
		SKB_TRUESIZE(skb_end_pointer(from) - from->head);
		copyfrags:
		WARN_ON_ONCE(delta < len);
		memcpy(skb_shinfo(to)->frags + skb_shinfo(to)->nr_frags,
		skb_shinfo(from)->frags,
		skb_shinfo(from)->nr_frags * sizeof(skb_frag_t));
		@@ -4600,7 +4598,7 @@ copyfrags:
		skb_fill_page_desc(to, skb_shinfo(to)->nr_frags,
		page, offset, skb_headlen(from));
		*fragstolen = true;
		delta = len; /* we dont know real truesize... */
		delta = from->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));
		goto copyfrags;
		}
		return false;

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