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Message-ID: <CANn89iLW3_1SZV4EV3h2W45B_+b+R67fp40t8OaqpqLnVEhTew@mail.gmail.com>
Date: Tue, 11 Apr 2023 19:09:00 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: David Howells <dhowells@...hat.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>,
David Ahern <dsahern@...nel.org>,
Matthew Wilcox <willy@...radead.org>,
Al Viro <viro@...iv.linux.org.uk>,
Christoph Hellwig <hch@...radead.org>,
Jens Axboe <axboe@...nel.dk>, Jeff Layton <jlayton@...nel.org>,
Christian Brauner <brauner@...nel.org>,
Chuck Lever III <chuck.lever@...cle.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH net-next v6 07/18] tcp: Support MSG_SPLICE_PAGES
On Tue, Apr 11, 2023 at 6:09 PM David Howells <dhowells@...hat.com> wrote:
>
> Make TCP's sendmsg() support MSG_SPLICE_PAGES. This causes pages to be
> spliced or copied (if it cannot be spliced) from the source iterator.
>
> This allows ->sendpage() to be replaced by something that can handle
> multiple multipage folios in a single transaction.
>
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Eric Dumazet <edumazet@...gle.com>
> cc: "David S. Miller" <davem@...emloft.net>
> cc: David Ahern <dsahern@...nel.org>
> cc: Jakub Kicinski <kuba@...nel.org>
> cc: Paolo Abeni <pabeni@...hat.com>
> cc: Jens Axboe <axboe@...nel.dk>
> cc: Matthew Wilcox <willy@...radead.org>
> cc: netdev@...r.kernel.org
> ---
>
> Notes:
> ver #6)
> - Use common helper.
>
> net/ipv4/tcp.c | 43 ++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 36 insertions(+), 7 deletions(-)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index fd68d49490f2..0b2213da5aaf 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1221,7 +1221,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
> int flags, err, copied = 0;
> int mss_now = 0, size_goal, copied_syn = 0;
> int process_backlog = 0;
> - bool zc = false;
> + int zc = 0;
> long timeo;
>
> flags = msg->msg_flags;
> @@ -1232,17 +1232,22 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
> if (msg->msg_ubuf) {
> uarg = msg->msg_ubuf;
> net_zcopy_get(uarg);
> - zc = sk->sk_route_caps & NETIF_F_SG;
> + if (sk->sk_route_caps & NETIF_F_SG)
> + zc = 1;
zc is set to 0, 1, MSG_ZEROCOPY , MSG_SPLICE_PAGES
I find this a bit confusing. Maybe use a private enum ?
> } else if (sock_flag(sk, SOCK_ZEROCOPY)) {
> uarg = msg_zerocopy_realloc(sk, size, skb_zcopy(skb));
> if (!uarg) {
> err = -ENOBUFS;
> goto out_err;
> }
> - zc = sk->sk_route_caps & NETIF_F_SG;
> - if (!zc)
> + if (sk->sk_route_caps & NETIF_F_SG)
> + zc = MSG_ZEROCOPY;
> + else
> uarg_to_msgzc(uarg)->zerocopy = 0;
> }
> + } else if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES) && size) {
> + if (sk->sk_route_caps & NETIF_F_SG)
> + zc = MSG_SPLICE_PAGES;
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