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Date:   Tue, 28 Jul 2020 23:34:17 -0700
From:   Josh Triplett <josh@joshtriplett.org>
To:     Pavel Machek <pavel@ucw.cz>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        alex.gaynor@gmail.com, Greg KH <gregkh@linuxfoundation.org>,
        geofft@ldpreload.com, jbaublitz@redhat.com,
        Masahiro Yamada <masahiroy@kernel.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Kees Cook <keescook@chromium.org>
Subject: Re: Linux kernel in-tree Rust support
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On Tue, Jul 28, 2020 at 10:40:38PM +0200, Pavel Machek wrote:
> > We just need to make sure that any kernel CI infrastructure tests that
> > right away, then, so that failures don't get introduced by a patch from
> > someone without a Rust toolchain and not noticed until someone with a
> > Rust toolchain tests it.
> 
> So... I'm fan of Rust, but while trying to use it one thing was obvious: it
> takes _significantly_ longer than C to compile and needs gigabyte a lot of RAM.
> 
> Kernel is quite big project, can CI infrastructure handle additional load?
> 
> Will developers see significantly longer compile times when Rust is widespread?

I wouldn't expect the addition of Rust to the kernel to substantially
impact overall build time; on balance, I'd expect the major bottleneck
in kernel builds to continue to be linking and other serialized steps,
not compiling and other highly parallel steps.

There are also *many* things that can be done to improve Rust build time
in a project. And I don't expect that in-kernel Rust will have many
dependencies on third-party crates (since they'd need to be checked into
the tree).