[RFC PATCH v2 43/48] kcm: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage

David Howells
2023-03-29T14:23:16Z

When transmitting data, call down into TCP using a single sendmsg with
MSG_SPLICE_PAGES to indicate that content should be spliced rather than
performing several sendmsg and sendpage calls to transmit header, data
pages and trailer.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Tom Herbert <tom@herbertland.com>
cc: Tom Herbert <tom@quantonium.net>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: netdev@vger.kernel.org
---
net/kcm/kcmsock.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index cfe828bd7fc6..819259149952 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -641,6 +641,10 @@ static int kcm_write_msgs(struct kcm_sock *kcm)

for (fragidx = 0; fragidx < skb_shinfo(skb)->nr_frags;
fragidx++) {
+ struct bio_vec bvec;
+ struct msghdr msg = {
+ .msg_flags = MSG_DONTWAIT | MSG_SPLICE_PAGES,
+ };
skb_frag_t *frag;

frag_offset = 0;
@@ -651,11 +655,12 @@ static int kcm_write_msgs(struct kcm_sock *kcm)
goto out;
}

- ret = kernel_sendpage(psock->sk->sk_socket,
- skb_frag_page(frag),
- skb_frag_off(frag) + frag_offset,
- skb_frag_size(frag) - frag_offset,
- MSG_DONTWAIT);
+ bvec_set_page(&bvec,
+ skb_frag_page(frag),
+ skb_frag_size(frag) - frag_offset,
+ skb_frag_off(frag) + frag_offset);
+ iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, bvec.bv_len);
+ ret = sock_sendmsg(psock->sk->sk_socket, &msg);
if (ret <= 0) {
if (ret == -EAGAIN) {
/* Save state to try again when there's