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kcm: Convert kcm_sendpage() to use MSG_SPLICE_PAGES
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Convert kcm_sendpage() to use sendmsg() with MSG_SPLICE_PAGES rather than
directly splicing in the pages itself.

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: Tom Herbert <tom@herbertland.com>
cc: Tom Herbert <tom@quantonium.net>
cc: Cong Wang <cong.wang@bytedance.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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David Howells authored and Jakub Kicinski committed Jun 6, 2023
1 parent 2b03bca commit 5bb3a5c
Showing 1 changed file with 18 additions and 143 deletions.
161 changes: 18 additions & 143 deletions net/kcm/kcmsock.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -761,149 +761,6 @@ static void kcm_push(struct kcm_sock *kcm)
kcm_write_msgs(kcm);
}

static ssize_t kcm_sendpage(struct socket *sock, struct page *page,
int offset, size_t size, int flags)

{
struct sock *sk = sock->sk;
struct kcm_sock *kcm = kcm_sk(sk);
struct sk_buff *skb = NULL, *head = NULL;
long timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
bool eor;
int err = 0;
int i;

if (flags & MSG_SENDPAGE_NOTLAST)
flags |= MSG_MORE;

/* No MSG_EOR from splice, only look at MSG_MORE */
eor = !(flags & MSG_MORE);

lock_sock(sk);

sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);

err = -EPIPE;
if (sk->sk_err)
goto out_error;

if (kcm->seq_skb) {
/* Previously opened message */
head = kcm->seq_skb;
skb = kcm_tx_msg(head)->last_skb;
i = skb_shinfo(skb)->nr_frags;

if (skb_can_coalesce(skb, i, page, offset)) {
skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], size);
skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG;
goto coalesced;
}

if (i >= MAX_SKB_FRAGS) {
struct sk_buff *tskb;

tskb = alloc_skb(0, sk->sk_allocation);
while (!tskb) {
kcm_push(kcm);
err = sk_stream_wait_memory(sk, &timeo);
if (err)
goto out_error;
}

if (head == skb)
skb_shinfo(head)->frag_list = tskb;
else
skb->next = tskb;

skb = tskb;
skb->ip_summed = CHECKSUM_UNNECESSARY;
i = 0;
}
} else {
/* Call the sk_stream functions to manage the sndbuf mem. */
if (!sk_stream_memory_free(sk)) {
kcm_push(kcm);
set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
err = sk_stream_wait_memory(sk, &timeo);
if (err)
goto out_error;
}

head = alloc_skb(0, sk->sk_allocation);
while (!head) {
kcm_push(kcm);
err = sk_stream_wait_memory(sk, &timeo);
if (err)
goto out_error;
}

skb = head;
i = 0;
}

get_page(page);
skb_fill_page_desc_noacc(skb, i, page, offset, size);
skb_shinfo(skb)->flags |= SKBFL_SHARED_FRAG;

coalesced:
skb->len += size;
skb->data_len += size;
skb->truesize += size;
sk->sk_wmem_queued += size;
sk_mem_charge(sk, size);

if (head != skb) {
head->len += size;
head->data_len += size;
head->truesize += size;
}

if (eor) {
bool not_busy = skb_queue_empty(&sk->sk_write_queue);

/* Message complete, queue it on send buffer */
__skb_queue_tail(&sk->sk_write_queue, head);
kcm->seq_skb = NULL;
KCM_STATS_INCR(kcm->stats.tx_msgs);

if (flags & MSG_BATCH) {
kcm->tx_wait_more = true;
} else if (kcm->tx_wait_more || not_busy) {
err = kcm_write_msgs(kcm);
if (err < 0) {
/* We got a hard error in write_msgs but have
* already queued this message. Report an error
* in the socket, but don't affect return value
* from sendmsg
*/
pr_warn("KCM: Hard failure on kcm_write_msgs\n");
report_csk_error(&kcm->sk, -err);
}
}
} else {
/* Message not complete, save state */
kcm->seq_skb = head;
kcm_tx_msg(head)->last_skb = skb;
}

KCM_STATS_ADD(kcm->stats.tx_bytes, size);

release_sock(sk);
return size;

out_error:
kcm_push(kcm);

err = sk_stream_error(sk, flags, err);

/* make sure we wake any epoll edge trigger waiter */
if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 && err == -EAGAIN))
sk->sk_write_space(sk);

release_sock(sk);
return err;
}

static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
{
struct sock *sk = sock->sk;
Expand Down Expand Up @@ -1111,6 +968,24 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
return err;
}

static ssize_t kcm_sendpage(struct socket *sock, struct page *page,
int offset, size_t size, int flags)

{
struct bio_vec bvec;
struct msghdr msg = { .msg_flags = flags | MSG_SPLICE_PAGES, };

if (flags & MSG_SENDPAGE_NOTLAST)
msg.msg_flags |= MSG_MORE;

if (flags & MSG_OOB)
return -EOPNOTSUPP;

bvec_set_page(&bvec, page, size, offset);
iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
return kcm_sendmsg(sock, &msg, size);
}

static int kcm_recvmsg(struct socket *sock, struct msghdr *msg,
size_t len, int flags)
{
Expand Down

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