Subject: [PATCH net-next 2/2] tcp: adjust rcv zerocopy hints based on frag sizes

From: Soheil Hassas Yeganeh <[email-masked]>
Date: Wed, 26 Sep 2018 16:57:04 -0400

From: Soheil Hassas Yeganeh <[email-masked]>

When SKBs are coalesced, we can have SKBs with different
frag sizes. Some with PAGE_SIZE and some not with PAGE_SIZE.
Since recv_skip_hint is always set to the full SKB size,
it can overestimate the amount that should be read using
normal read for coalesced packets.

Change the recv_skip_hint so that it only includes the first
frags that are not of PAGE_SIZE.

Signed-off-by: Soheil Hassas Yeganeh <[email-masked]>
Signed-off-by: Eric Dumazet <[email-masked]>
---
 net/ipv4/tcp.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 3e17501fc1a1..cdbd423bdeb4 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1805,8 +1805,17 @@ static int tcp_zerocopy_receive(struct sock *sk,
 				frags++;
 			}
 		}
-		if (frags->size != PAGE_SIZE || frags->page_offset)
+		if (frags->size != PAGE_SIZE || frags->page_offset) {
+			int remaining = zc->recv_skip_hint;
+
+			while (remaining && (frags->size != PAGE_SIZE ||
+					     frags->page_offset)) {
+				remaining -= frags->size;
+				frags++;
+			}
+			zc->recv_skip_hint -= remaining;
 			break;
+		}
 		ret = vm_insert_page(vma, address + length,
 				     skb_frag_page(frags));
 		if (ret)
-- 
2.19.0.605.g01d371f741-goog