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Commit 329033f6 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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tcp: makes tcp_try_coalesce aware of skb->head_frag 



TCP coalesce can check if skb to be merged has its skb->head mapped to a
page fragment, instead of a kmalloc() area.

We had to disable coalescing in this case, for performance reasons.

We 'upgrade' skb->head as a fragment in itself.

This reduces number of cache misses when user makes its copies, since a
less sk_buff are fetched.

This makes receive and ofo queues shorter and thus reduce cache line
misses in TCP stack.

This is a followup of patch "net: allow skb->head to be a page fragment"

Tested with tg3 nic, with GRO on or off. We can see "TCPRcvCoalesce"
counter being incremented.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: Matt Carlson <mcarlson@broadcom.com>
Cc: Michael Chan <mchan@broadcom.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d7e8883c

net/ipv4/tcp_input.c

+43 −12
Original line number Diff line number Diff line
@@ -4464,10 +4464,12 @@ static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size) 
 */

static bool tcp_try_coalesce(struct sock *sk,

			     struct sk_buff *to,

			     struct sk_buff *from)

			     struct sk_buff *from,

			     bool *fragstolen)

{

	int len = from->len;

	int delta, len = from->len;



	*fragstolen = false;

	if (tcp_hdr(from)->fin)

		return false;

	if (len <= skb_tailroom(to)) {
@@ -4478,15 +4480,19 @@ merge: 
		TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;

		return true;

	}



	if (skb_has_frag_list(to) || skb_has_frag_list(from))

		return false;



	if (skb_headlen(from) == 0 &&

	    !skb_has_frag_list(to) &&

	    !skb_has_frag_list(from) &&

	    (skb_shinfo(to)->nr_frags +

	     skb_shinfo(from)->nr_frags <= MAX_SKB_FRAGS)) {

		int delta = from->truesize - ksize(from->head) -

		WARN_ON_ONCE(from->head_frag);

		delta = from->truesize - ksize(from->head) -

			SKB_DATA_ALIGN(sizeof(struct sk_buff));



		WARN_ON_ONCE(delta < len);

copyfrags:

		memcpy(skb_shinfo(to)->frags + skb_shinfo(to)->nr_frags,

		       skb_shinfo(from)->frags,

		       skb_shinfo(from)->nr_frags * sizeof(skb_frag_t));
@@ -4499,6 +4505,20 @@ merge: 
		to->data_len += len;

		goto merge;

	}

	if (from->head_frag) {

		struct page *page;

		unsigned int offset;



		if (skb_shinfo(to)->nr_frags + skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS)

			return false;

		page = virt_to_head_page(from->head);

		offset = from->data - (unsigned char *)page_address(page);

		skb_fill_page_desc(to, skb_shinfo(to)->nr_frags,

				   page, offset, skb_headlen(from));

		*fragstolen = true;

		delta = len; /* we dont know real truesize... */

		goto copyfrags;

	}

	return false;

}
@@ -4540,9 +4560,14 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb) 
	end_seq = TCP_SKB_CB(skb)->end_seq;



	if (seq == TCP_SKB_CB(skb1)->end_seq) {

		if (!tcp_try_coalesce(sk, skb1, skb)) {

		bool fragstolen;



		if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) {

			__skb_queue_after(&tp->out_of_order_queue, skb1, skb);

		} else {

			if (fragstolen)

				kmem_cache_free(skbuff_head_cache, skb);

			else

				__kfree_skb(skb);

			skb = NULL;

		}
@@ -4626,6 +4651,7 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) 
	const struct tcphdr *th = tcp_hdr(skb);

	struct tcp_sock *tp = tcp_sk(sk);

	int eaten = -1;

	bool fragstolen = false;



	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)

		goto drop;
@@ -4672,7 +4698,9 @@ queue_and_out: 
				goto drop;



			tail = skb_peek_tail(&sk->sk_receive_queue);

			eaten = (tail && tcp_try_coalesce(sk, tail, skb)) ? 1 : 0;

			eaten = (tail &&

				 tcp_try_coalesce(sk, tail, skb,

						  &fragstolen)) ? 1 : 0;

			if (eaten <= 0) {

				skb_set_owner_r(skb, sk);

				__skb_queue_tail(&sk->sk_receive_queue, skb);
@@ -4699,9 +4727,12 @@ queue_and_out: 


		tcp_fast_path_check(sk);



		if (eaten > 0)

		if (eaten > 0) {

			if (fragstolen)

				kmem_cache_free(skbuff_head_cache, skb);

			else

				__kfree_skb(skb);

		else if (!sock_flag(sk, SOCK_DEAD))

		} else if (!sock_flag(sk, SOCK_DEAD))

			sk->sk_data_ready(sk, 0);

		return;

	}