linux-kernel - Re: [PATCH 5/7] rust: file: add `Kuid` wrapper

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Date:   Fri, 8 Dec 2023 18:37:50 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     comex <comexk@...il.com>, Christian Brauner <brauner@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
        rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 5/7] rust: file: add `Kuid` wrapper

On Fri, Dec 8, 2023 at 6:09 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> On paper, nothing comes to mind.  No promises though.

Thanks Nick -- that is useful nevertheless.

> From a build system perspective, I'd rather just point users towards
> LTO if they have this concern.  We support full and thin lto.  This
> proposal would add a third variant for just rust drivers.  Each
> variation on LTO has a maintenance cost and each have had their own
> distinct fun bugs in the past.  Not sure an additional variant is
> worth the maintenance cost, even if it's technically feasible.

I was thinking it would be something always done for Rust object
files: under a normal "no LTO" build, the Rust object files would
always get the cross-language inlining done and therefore no extra
dimension in the matrix. Would that help?

I think it is worth at least considering, given there is also a
non-trivial amount of performance to gain if we always do it, e.g.
Andreas wanted it for non-LTO kernel for this reason.

Cheers,
Miguel