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Message-ID: <CAOi1vP9vjLfk3W+AJFeexC93jqPaPUn2dD_4NrzxwoZTbYfOnw@mail.gmail.com>
Date: Sun, 25 Jun 2023 14:20:26 +0200
From: Ilya Dryomov <idryomov@...il.com>
To: David Howells <dhowells@...hat.com>
Cc: netdev@...r.kernel.org, Alexander Duyck <alexander.duyck@...il.com>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
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>, Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Xiubo Li <xiubli@...hat.com>,
Jeff Layton <jlayton@...nel.org>, ceph-devel@...r.kernel.org
Subject: Re: [PATCH net-next v5 03/16] ceph: Use sendmsg(MSG_SPLICE_PAGES)
rather than sendpage
On Sat, Jun 24, 2023 at 12:55 AM David Howells <dhowells@...hat.com> wrote:
>
> Use sendmsg() and MSG_SPLICE_PAGES rather than sendpage in ceph when
> transmitting data. For the moment, this can only transmit one page at a
> time because of the architecture of net/ceph/, but if
> write_partial_message_data() can be given a bvec[] at a time by the
> iteration code, this would allow pages to be sent in a batch.
>
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Ilya Dryomov <idryomov@...il.com>
> cc: Xiubo Li <xiubli@...hat.com>
> cc: Jeff Layton <jlayton@...nel.org>
> cc: "David S. Miller" <davem@...emloft.net>
> cc: Eric Dumazet <edumazet@...gle.com>
> 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: ceph-devel@...r.kernel.org
> cc: netdev@...r.kernel.org
> ---
>
> Notes:
> ver #5)
> - Switch condition for setting MSG_MORE in write_partial_message_data()
>
> net/ceph/messenger_v1.c | 60 ++++++++++++++---------------------------
> 1 file changed, 20 insertions(+), 40 deletions(-)
>
> diff --git a/net/ceph/messenger_v1.c b/net/ceph/messenger_v1.c
> index d664cb1593a7..814579f27f04 100644
> --- a/net/ceph/messenger_v1.c
> +++ b/net/ceph/messenger_v1.c
> @@ -74,37 +74,6 @@ static int ceph_tcp_sendmsg(struct socket *sock, struct kvec *iov,
> return r;
> }
>
> -/*
> - * @more: either or both of MSG_MORE and MSG_SENDPAGE_NOTLAST
> - */
> -static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
> - int offset, size_t size, int more)
> -{
> - ssize_t (*sendpage)(struct socket *sock, struct page *page,
> - int offset, size_t size, int flags);
> - int flags = MSG_DONTWAIT | MSG_NOSIGNAL | more;
> - int ret;
> -
> - /*
> - * sendpage cannot properly handle pages with page_count == 0,
> - * we need to fall back to sendmsg if that's the case.
> - *
> - * Same goes for slab pages: skb_can_coalesce() allows
> - * coalescing neighboring slab objects into a single frag which
> - * triggers one of hardened usercopy checks.
> - */
> - if (sendpage_ok(page))
> - sendpage = sock->ops->sendpage;
> - else
> - sendpage = sock_no_sendpage;
> -
> - ret = sendpage(sock, page, offset, size, flags);
> - if (ret == -EAGAIN)
> - ret = 0;
> -
> - return ret;
> -}
> -
> static void con_out_kvec_reset(struct ceph_connection *con)
> {
> BUG_ON(con->v1.out_skip);
> @@ -464,7 +433,6 @@ static int write_partial_message_data(struct ceph_connection *con)
> struct ceph_msg *msg = con->out_msg;
> struct ceph_msg_data_cursor *cursor = &msg->cursor;
> bool do_datacrc = !ceph_test_opt(from_msgr(con->msgr), NOCRC);
> - int more = MSG_MORE | MSG_SENDPAGE_NOTLAST;
> u32 crc;
>
> dout("%s %p msg %p\n", __func__, con, msg);
> @@ -482,6 +450,10 @@ static int write_partial_message_data(struct ceph_connection *con)
> */
> crc = do_datacrc ? le32_to_cpu(msg->footer.data_crc) : 0;
> while (cursor->total_resid) {
> + struct bio_vec bvec;
> + struct msghdr msghdr = {
> + .msg_flags = MSG_SPLICE_PAGES,
Hi David,
This appears to be losing MSG_DONTWAIT | MSG_NOSIGNAL flags which were
set previously?
> + };
> struct page *page;
> size_t page_offset;
> size_t length;
> @@ -493,10 +465,13 @@ static int write_partial_message_data(struct ceph_connection *con)
> }
>
> page = ceph_msg_data_next(cursor, &page_offset, &length);
> - if (length == cursor->total_resid)
> - more = MSG_MORE;
> - ret = ceph_tcp_sendpage(con->sock, page, page_offset, length,
> - more);
> + if (length != cursor->total_resid)
> + msghdr.msg_flags |= MSG_MORE;
> +
> + bvec_set_page(&bvec, page, length, page_offset);
> + iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, length);
> +
> + ret = sock_sendmsg(con->sock, &msghdr);
> if (ret <= 0) {
And this is losing munging -EAGAIN -> 0?
> if (do_datacrc)
> msg->footer.data_crc = cpu_to_le32(crc);
> @@ -526,7 +501,10 @@ static int write_partial_message_data(struct ceph_connection *con)
> */
> static int write_partial_skip(struct ceph_connection *con)
> {
> - int more = MSG_MORE | MSG_SENDPAGE_NOTLAST;
> + struct bio_vec bvec;
> + struct msghdr msghdr = {
> + .msg_flags = MSG_SPLICE_PAGES | MSG_MORE,
> + };
> int ret;
>
> dout("%s %p %d left\n", __func__, con, con->v1.out_skip);
> @@ -534,9 +512,11 @@ static int write_partial_skip(struct ceph_connection *con)
> size_t size = min(con->v1.out_skip, (int)PAGE_SIZE);
>
> if (size == con->v1.out_skip)
> - more = MSG_MORE;
> - ret = ceph_tcp_sendpage(con->sock, ceph_zero_page, 0, size,
> - more);
> + msghdr.msg_flags &= ~MSG_MORE;
> + bvec_set_page(&bvec, ZERO_PAGE(0), size, 0);
> + iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, size);
> +
> + ret = sock_sendmsg(con->sock, &msghdr);
> if (ret <= 0)
Same here... I would suggest that you keep ceph_tcp_sendpage() function
and make only minimal modifications to avoid regressions.
Thanks,
Ilya
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