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Date: Mon, 7 Dec 2020 17:39:40 -0700 From: David Ahern <dsahern@...il.com> To: Boris Pismenny <borisp@...lanox.com>, kuba@...nel.org, davem@...emloft.net, saeedm@...dia.com, hch@....de, sagi@...mberg.me, axboe@...com, kbusch@...nel.org, viro@...iv.linux.org.uk, edumazet@...gle.com Cc: boris.pismenny@...il.com, linux-nvme@...ts.infradead.org, netdev@...r.kernel.org, benishay@...dia.com, ogerlitz@...dia.com, yorayz@...dia.com, Ben Ben-Ishay <benishay@...lanox.com>, Or Gerlitz <ogerlitz@...lanox.com>, Yoray Zack <yorayz@...lanox.com> Subject: Re: [PATCH v1 net-next 01/15] iov_iter: Skip copy in memcpy_to_page if src==dst 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.
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