[RFC PATCH 03/28] tcp: Support MSG_SPLICE_PAGES
From: David Howells <dhowells@redhat.com>
Date: 2023-03-16 15:27:40
Also in:
linux-fsdevel, linux-mm, lkml
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
Make TCP's sendmsg() support MSG_SPLICE_PAGES. This causes pages to be spliced from the source iterator if possible (the iterator must be ITER_BVEC and the pages must be spliceable). This allows ->sendpage() to be replaced by something that can handle multiple multipage folios in a single transaction. Signed-off-by: David Howells <dhowells@redhat.com> cc: Eric Dumazet <edumazet@google.com> cc: "David S. Miller" <davem@davemloft.net> 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/ipv4/tcp.c | 59 +++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 53 insertions(+), 6 deletions(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 288693981b00..77c0c69208a5 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c@@ -1220,7 +1220,7 @@ 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;
@@ -1231,17 +1231,24 @@ 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; } 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 = 1; + else uarg_to_msgzc(uarg)->zerocopy = 0; } + } else if (unlikely(flags & MSG_SPLICE_PAGES) && size) { + if (!iov_iter_is_bvec(&msg->msg_iter)) + return -EINVAL; + if (sk->sk_route_caps & NETIF_F_SG) + zc = 2; } if (unlikely(flags & MSG_FASTOPEN || inet_sk(sk)->defer_connect) &&
@@ -1345,7 +1352,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) if (copy > msg_data_left(msg)) copy = msg_data_left(msg); - if (!zc) { + if (zc == 0) { bool merge = true; int i = skb_shinfo(skb)->nr_frags; struct page_frag *pfrag = sk_page_frag(sk);
@@ -1390,7 +1397,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) page_ref_inc(pfrag->page); } pfrag->offset += copy; - } else { + } else if (zc == 1) { /* First append to a fragless skb builds initial * pure zerocopy skb */
@@ -1411,6 +1418,46 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) if (err < 0) goto do_error; copy = err; + } else if (zc == 2) { + /* Splice in data. */ + const struct bio_vec *bv = msg->msg_iter.bvec; + size_t seg = iov_iter_single_seg_count(&msg->msg_iter); + size_t off = bv->bv_offset + msg->msg_iter.iov_offset; + bool can_coalesce; + int i = skb_shinfo(skb)->nr_frags; + + if (copy > seg) + copy = seg; + + can_coalesce = skb_can_coalesce(skb, i, bv->bv_page, off); + if (!can_coalesce && i >= READ_ONCE(sysctl_max_skb_frags)) { + tcp_mark_push(tp, skb); + goto new_segment; + } + if (tcp_downgrade_zcopy_pure(sk, skb)) + goto wait_for_space; + + copy = tcp_wmem_schedule(sk, copy); + if (!copy) + goto wait_for_space; + + if (can_coalesce) { + skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy); + } else { + get_page(bv->bv_page); + skb_fill_page_desc_noacc(skb, i, bv->bv_page, off, copy); + } + iov_iter_advance(&msg->msg_iter, copy); + + if (!(flags & MSG_NO_SHARED_FRAGS)) + skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG; + + skb->len += copy; + skb->data_len += copy; + skb->truesize += copy; + sk_wmem_queued_add(sk, copy); + sk_mem_charge(sk, copy); + } if (!copied)