MIME-Version: 1.0
References: <0cfd9f02-dea7-90e2-e932-c8129b6013c7@samba.org>
 <CAHk-=wj8rthcQ9gQbvkMzeFt0iymq+CuOzmidx3Pm29Lg+W0gg@mail.gmail.com>
 <20230210021603.GA2825702@dread.disaster.area> <20230210040626.GB2825702@dread.disaster.area>
 <Y+XLuYh+kC+4wTRi@casper.infradead.org> <20230210065747.GD2825702@dread.disaster.area>
 <CALCETrWjJisipSJA7tPu+h6B2gs3m+g0yPhZ4z+Atod+WOMkZg@mail.gmail.com>
 <CAHk-=wj66F6CdJUAAjqigXMBy7gHquFMzPNAwKCgkrb2mF6U7w@mail.gmail.com>
 <CALCETrU-9Wcb_zCsVWr24V=uCA0+c6x359UkJBOBgkbq+UHAMA@mail.gmail.com>
 <CAHk-=wjQZWMeQ9OgXDNepf+TLijqj0Lm0dXWwWzDcbz6o7yy_g@mail.gmail.com>
 <CALCETrWuRHWh5XFn8M8qx5z0FXAGHH=ysb+c6J+cqbYyTAHvhw@mail.gmail.com>
 <CAHk-=wjuXvF1cA=gJod=-6k4ypbEmOczFFDKriUpOVKy9dTJWQ@mail.gmail.com>
 <CALCETrUXYts5BRZKb25MVaWPk2mz34fKSqCR++SM382kSYLnJw@mail.gmail.com>
 <CAHk-=wgA=rB=7M_Fe3n9UkoW_7dqdUT2D=yb94=6GiGXEuAHDA@mail.gmail.com>
 <1dd85095-c18c-ed3e-38b7-02f4d13d9bd6@kernel.dk> <CAHk-=wiszt6btMPeT5UFcS=0=EVr=0injTR75KsvN8WetwQwkA@mail.gmail.com>
 <fe8252bd-17bd-850d-dcd0-d799443681e9@kernel.dk>
In-Reply-To: <fe8252bd-17bd-850d-dcd0-d799443681e9@kernel.dk>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 10 Feb 2023 12:44:56 -0800
Message-ID: <CAHk-=wiJ0QKKiORkVr8n345sPp=aHbrLTLu6CQ-S0XqWJ-kJ1A@mail.gmail.com>
Subject: Re: copy on write for splice() from file to pipe?
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Dave Chinner <david@fromorbit.com>,
        Matthew Wilcox <willy@infradead.org>,
        Stefan Metzmacher <metze@samba.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux API Mailing List <linux-api@vger.kernel.org>,
        io-uring <io-uring@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Samba Technical <samba-technical@lists.samba.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Feb 10, 2023 at 12:39 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> Right, I'm referencing doing zerocopy data sends with io_uring, using
> IORING_OP_SEND_ZC. This isn't from a file, it's from a memory location,
> but the important bit here is the split notifications and how you
> could wire up a OP_SENDFILE similarly to what Andy described.

Sure, I think it's much more reasonable with io_uring than with splice itself.

So I was mainly just reacting to the "strict-splice" thing where Andy
was talking about tracking the page refcounts. I don't think anything
like that can be done at a splice() level, but higher levels that
actually know about the whole IO might be able to do something like
that.

Maybe we're just talking past each other.

             Linus