linux-kernel - Re: [PATCH v9 12/27] rust: add `kernel` crate

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Message-ID: <Yu6BXwtPZwYPIDT6@casper.infradead.org>
Date:   Sat, 6 Aug 2022 15:57:35 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Konstantin Shelekhin <k.shelekhin@...ro.com>, ojeda@...nel.org,
        alex.gaynor@...il.com, ark.email@...il.com,
        bjorn3_gh@...tonmail.com, bobo1239@....de, bonifaido@...il.com,
        boqun.feng@...il.com, davidgow@...gle.com, dev@...lasmohrin.de,
        dsosnowski@...snowski.pl, foxhlchen@...il.com, gary@...yguo.net,
        geofft@...reload.com, gregkh@...uxfoundation.org,
        jarkko@...nel.org, john.m.baublitz@...il.com,
        leseulartichaut@...il.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, m.falkowski@...sung.com,
        me@...enk.de, milan@...verde.com, mjmouse9999@...il.com,
        patches@...ts.linux.dev, rust-for-linux@...r.kernel.org,
        thesven73@...il.com, torvalds@...ux-foundation.org,
        viktor@...ar.de, wedsonaf@...gle.com,
        Andreas Hindborg <andreas.hindborg@....com>
Subject: Re: [PATCH v9 12/27] rust: add `kernel` crate

On Sat, Aug 06, 2022 at 01:22:52PM +0200, Miguel Ojeda wrote:
> On Sat, Aug 6, 2022 at 12:25 PM Konstantin Shelekhin
> <k.shelekhin@...ro.com> wrote:
> >
> > I sense possible problems here. It's common for a kernel code to pass
> > flags during memory allocations.
> 
> Yes, of course. We will support this, but how exactly it will look
> like, to what extent upstream Rust's `alloc` could support our use
> cases, etc. has been on discussion for a long time.
> 
> For instance, see https://github.com/Rust-for-Linux/linux/pull/815 for
> a potential extension trait approach with no allocator carried on the
> type that Andreas wrote after a discussion in the last informal call:
> 
>     let a = Box::try_new_atomic(101)?;

Something I've been wondering about for a while is ...

struct task_struct {
...
+	gfp_t gfp_flags;
...
};

We've already done some work towards this with the scoped allocation
API for NOIO and NOFS, but having spin_lock() turn current->gfp_flags
into GFP_ATOMIC might not be the worst idea in the world.