[PATCH v1 net-next 01/15] iov_iter: Skip copy in memcpy_to_page if src==dst

[David Ahern]

On 12/7/20 2:06 PM, Boris Pismenny wrote:
> When using direct data placement the NIC writes some of the payload
> directly to the destination buffer, and constructs the SKB such that it
> points to this data. As a result, the skb_copy datagram_iter call will
> attempt to copy data when it is not necessary.
> 
> This patch adds a check to avoid this copy, and a static_key to enabled
> it when TCP direct data placement is possible.
> 

Why not mark the skb as ZEROCOPY -- an Rx version of the existing
SKBTX_DEV_ZEROCOPY and skb_shared_info->tx_flags? Use that as a generic
way of indicating to the stack what is happening.