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Date:   Fri, 5 May 2023 06:28:04 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Andreas Hindborg <nmi@metaspace.dk>
Cc:     Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
        Keith Busch <kbusch@kernel.org>,
        Damien Le Moal <Damien.LeMoal@wdc.com>,
        Hannes Reinecke <hare@suse.de>,
        lsf-pc@lists.linux-foundation.org, rust-for-linux@vger.kernel.org,
        linux-block@vger.kernel.org, Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
        Benno Lossin <benno.lossin@proton.me>,
        open list <linux-kernel@vger.kernel.org>, gost.dev@samsung.com
Subject: Re: [RFC PATCH 01/11] rust: add radix tree abstraction
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On Fri, May 05, 2023 at 06:49:49AM +0200, Andreas Hindborg wrote:
> 
> Matthew Wilcox <willy@infradead.org> writes:
> 
> > On Wed, May 03, 2023 at 11:06:58AM +0200, Andreas Hindborg wrote:
> >> From: Andreas Hindborg <a.hindborg@samsung.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.