Re: [PATCH v3] skbuff: Add MSG_MORE flag to optimize large packet transmission

[Eric Dumazet]

On Sun, Jul 6, 2025 at 11:17 PM Feng Yang <yangfeng59949@xxxxxxx> wrote:

>
> So do I need to resend the v2 version again (https://lore.kernel.org/all/20250627094406.100919-1-yangfeng59949@xxxxxxx/),
> or is this version also inapplicable in some cases?

Or a V3 perhaps, limiting MSG_MORE hint to TCP sockets where it is
definitely safe.

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index d6420b74ea9c6a9c53a7c16634cce82a1cd1bbd3..dc440252a68e5e7bb0588ab230fbc5b7a656e220
100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3235,6 +3235,7 @@ typedef int (*sendmsg_func)(struct sock *sk,
struct msghdr *msg);
 static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
                           int len, sendmsg_func sendmsg, int flags)
 {
+       int more_hint = sk_is_tcp(sk) ? MSG_MORE : 0;
        unsigned int orig_len = len;
        struct sk_buff *head = skb;
        unsigned short fragidx;
@@ -3252,7 +3253,8 @@ static int __skb_send_sock(struct sock *sk,
struct sk_buff *skb, int offset,
                kv.iov_len = slen;
                memset(&msg, 0, sizeof(msg));
                msg.msg_flags = MSG_DONTWAIT | flags;
-
+               if (slen < len)
+                       msg.msg_flags |= more_hint;
                iov_iter_kvec(&msg.msg_iter, ITER_SOURCE, &kv, 1, slen);
                ret = INDIRECT_CALL_2(sendmsg, sendmsg_locked,
                                      sendmsg_unlocked, sk, &msg);
@@ -3292,6 +3294,8 @@ static int __skb_send_sock(struct sock *sk,
struct sk_buff *skb, int offset,
                                             flags,
                        };

+                       if (slen < len)
+                               msg.msg_flags |= more_hint;
                        bvec_set_page(&bvec, skb_frag_page(frag), slen,
                                      skb_frag_off(frag) + offset);
                        iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1,