linux-kernel - Re: [PATCH net-next v5 03/14] splice, net: Use sendmsg(MSG_SPLICE

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Message-ID: <20230607095541.586a3300@kernel.org>
Date:   Wed, 7 Jun 2023 09:55:41 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     netdev@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Chuck Lever <chuck.lever@...cle.com>,
        Boris Pismenny <borisp@...dia.com>,
        John Fastabend <john.fastabend@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5 03/14] splice, net: Use
 sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()

On Wed,  7 Jun 2023 15:05:48 +0100 David Howells wrote:
> Replace generic_splice_sendpage() + splice_from_pipe + pipe_to_sendpage()
> with a net-specific handler, splice_to_socket(), that calls sendmsg() with
> MSG_SPLICE_PAGES set instead of calling ->sendpage().
> 
> MSG_MORE is used to indicate if the sendmsg() is expected to be followed
> with more data.
> 
> This allows multiple pipe-buffer pages to be passed in a single call in a
> BVEC iterator, allowing the processing to be pushed down to a loop in the
> protocol driver.  This helps pave the way for passing multipage folios down
> too.
> 
> Protocols that haven't been converted to handle MSG_SPLICE_PAGES yet should
> just ignore it and do a normal sendmsg() for now - although that may be a
> bit slower as it may copy everything.

Reviewed-by: Jakub Kicinski <kuba@...nel.org>