Re: [PATCH net-next v5 04/16] ceph: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage()
From: Ilya Dryomov <idryomov@gmail.com>
Date: 2023-06-25 12:35:04
Also in:
ceph-devel, linux-mm, lkml
On Sat, Jun 24, 2023 at 12:55 AM David Howells [off-list ref] 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
Hi David, write_partial_message_data() is net/ceph/messenger_v1.c specific, so it doesn't apply here. I would suggest squashing the two net/ceph patches into one since even the titles are the same. Also, we tend to use "libceph: " prefix for net/ceph changes.
quoted hunk ↗ jump to hunk
iteration code, this would allow pages to be sent in a batch. Signed-off-by: David Howells <dhowells@redhat.com> cc: Ilya Dryomov <idryomov@gmail.com> cc: Xiubo Li <redacted> cc: Jeff Layton <jlayton@kernel.org> 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: ceph-devel@vger.kernel.org cc: netdev@vger.kernel.org --- net/ceph/messenger_v2.c | 91 +++++++++-------------------------------- 1 file changed, 19 insertions(+), 72 deletions(-)diff --git a/net/ceph/messenger_v2.c b/net/ceph/messenger_v2.c index 301a991dc6a6..87ac97073e75 100644 --- a/net/ceph/messenger_v2.c +++ b/net/ceph/messenger_v2.c@@ -117,91 +117,38 @@ static int ceph_tcp_recv(struct ceph_connection *con) return ret; } -static int do_sendmsg(struct socket *sock, struct iov_iter *it) -{ - struct msghdr msg = { .msg_flags = CEPH_MSG_FLAGS }; - int ret; - - msg.msg_iter = *it; - while (iov_iter_count(it)) { - ret = sock_sendmsg(sock, &msg); - if (ret <= 0) { - if (ret == -EAGAIN) - ret = 0; - return ret; - } - - iov_iter_advance(it, ret); - } - - WARN_ON(msg_data_left(&msg)); - return 1; -} - -static int do_try_sendpage(struct socket *sock, struct iov_iter *it) -{ - struct msghdr msg = { .msg_flags = CEPH_MSG_FLAGS }; - struct bio_vec bv; - int ret; - - if (WARN_ON(!iov_iter_is_bvec(it))) - return -EINVAL; - - while (iov_iter_count(it)) { - /* iov_iter_iovec() for ITER_BVEC */ - bvec_set_page(&bv, it->bvec->bv_page, - min(iov_iter_count(it), - it->bvec->bv_len - it->iov_offset), - it->bvec->bv_offset + it->iov_offset); - - /* - * 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(bv.bv_page)) { - ret = sock->ops->sendpage(sock, bv.bv_page, - bv.bv_offset, bv.bv_len, - CEPH_MSG_FLAGS); - } else { - iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bv, 1, bv.bv_len); - ret = sock_sendmsg(sock, &msg); - } - if (ret <= 0) { - if (ret == -EAGAIN) - ret = 0; - return ret; - } - - iov_iter_advance(it, ret); - } - - return 1; -} - /* * Write as much as possible. The socket is expected to be corked, - * so we don't bother with MSG_MORE/MSG_SENDPAGE_NOTLAST here. + * so we don't bother with MSG_MORE here. * * Return: - * 1 - done, nothing (else) to write + * >0 - done, nothing (else) to write
It would be nice to avoid making tweaks like this to the outer interface as part of switching to a new internal API.
* 0 - socket is full, need to wait
* <0 - error
*/
static int ceph_tcp_send(struct ceph_connection *con)
{
+ struct msghdr msg = {
+ .msg_iter = con->v2.out_iter,
+ .msg_flags = CEPH_MSG_FLAGS,
+ };
int ret;
+ if (WARN_ON(!iov_iter_is_bvec(&con->v2.out_iter)))
+ return -EINVAL;Previously, this WARN_ON + error applied only to the "try sendpage" path. There is a ton of kvec usage in net/ceph/messenger_v2.c, so I'm pretty sure that placing it here breaks everything.
+
+ if (con->v2.out_iter_sendpage)
+ msg.msg_flags |= MSG_SPLICE_PAGES;
+
dout("%s con %p have %zu try_sendpage %d\n", __func__, con,
iov_iter_count(&con->v2.out_iter), con->v2.out_iter_sendpage);
- if (con->v2.out_iter_sendpage)
- ret = do_try_sendpage(con->sock, &con->v2.out_iter);
- else
- ret = do_sendmsg(con->sock, &con->v2.out_iter);
+
+ ret = sock_sendmsg(con->sock, &msg);
+ if (ret > 0)
+ iov_iter_advance(&con->v2.out_iter, ret);
+ else if (ret == -EAGAIN)
+ ret = 0;Hrm, is sock_sendmsg() now guaranteed to exhaust the iterator (i.e. a "short write" is no longer possible)? Unless that is the case, this is not an equivalent transformation. This is actually the reason for
* Return: * 1 - done, nothing (else) to write
specification which you also tweaked. It doesn't make sense for
ceph_tcp_send() to return the number of bytes sent because the caller
expects everything to be sent when a positive number is returned.
Thanks,
Ilya