Commit c208bdb9 authored Oct 10, 2019 by Soheil Hassas Yeganeh Committed by David S. Miller Oct 13, 2019

tcp: improve recv_skip_hint for tcp_zerocopy_receive



tcp_zerocopy_receive() rounds down the zc->length a multiple of
PAGE_SIZE. This results in two issues:
- tcp_zerocopy_receive sets recv_skip_hint to the length of the
  receive queue if the zc->length input is smaller than the
  PAGE_SIZE, even though the data in receive queue could be
  zerocopied.
- tcp_zerocopy_receive would set recv_skip_hint of 0, in cases
  where we have a little bit of data after the perfectly-sized
  packets.

To fix these issues, do not store the rounded down value in
zc->length. Round down the length passed to zap_page_range(),
and return min(inq, zc->length) when the zap_range is 0.

Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 524900a2

net/ipv4/tcp.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -1739,8 +1739,8 @@ static int tcp_zerocopy_receive(struct sock *sk,
		struct tcp_zerocopy_receive *zc)
		{
		unsigned long address = (unsigned long)zc->address;
		u32 length = 0, seq, offset, zap_len;
		const skb_frag_t *frags = NULL;
		u32 length = 0, seq, offset;
		struct vm_area_struct *vma;
		struct sk_buff *skb = NULL;
		struct tcp_sock *tp;
		@@ -1767,12 +1767,12 @@ static int tcp_zerocopy_receive(struct sock *sk,
		seq = tp->copied_seq;
		inq = tcp_inq(sk);
		zc->length = min_t(u32, zc->length, inq);
		zc->length &= ~(PAGE_SIZE - 1);
		if (zc->length) {
		zap_page_range(vma, address, zc->length);
		zap_len = zc->length & ~(PAGE_SIZE - 1);
		if (zap_len) {
		zap_page_range(vma, address, zap_len);
		zc->recv_skip_hint = 0;
		} else {
		zc->recv_skip_hint = inq;
		zc->recv_skip_hint = zc->length;
		}
		ret = 0;
		while (length + PAGE_SIZE <= zc->length) {

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