linux-kernel - Re: [RFC PATCH 01/11] rust: add radix tree abstraction

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Date:   Fri, 5 May 2023 06:28:04 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Andreas Hindborg <nmi@...aspace.dk>
Cc:     Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Keith Busch <kbusch@...nel.org>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Hannes Reinecke <hare@...e.de>,
        lsf-pc@...ts.linux-foundation.org, rust-for-linux@...r.kernel.org,
        linux-block@...r.kernel.org, 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>,
        open list <linux-kernel@...r.kernel.org>, gost.dev@...sung.com
Subject: Re: [RFC PATCH 01/11] rust: add radix tree abstraction

On Fri, May 05, 2023 at 06:49:49AM +0200, Andreas Hindborg wrote:
> 
> Matthew Wilcox <willy@...radead.org> writes:
> 
> > On Wed, May 03, 2023 at 11:06:58AM +0200, Andreas Hindborg wrote:
> >> From: Andreas Hindborg <a.hindborg@...sung.com>
> >> 
> >> Add abstractions for the C radix_tree. This abstraction allows Rust code to use
> >> the radix_tree as a map from `u64` keys to `ForeignOwnable` values.
> >
> > Please, no.  The XArray interface is the preferred one; the radix tree
> > is legacy.  Don't make Rust code use the radix tree.  It has the GFP
> > arguments in the wrong place, for one thing.
> 
> I have a similar argument to not using xarrray as to not using folios,
> see my other response. But the Rust xarray API is in the works [1].

But the radix tree API is simply a different (and worse) API to the
exact same data structure as the XArray.  Using the XArray instead of
the radix tree is still an apples-to-apples comparison.