linux-kernel - Re: [PATCH v3 1/3] rust: maple

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Message-ID: <aLa4rNojDIeShIrw@google.com>
Date: Tue, 2 Sep 2025 09:28:12 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Miguel Ojeda <ojeda@...nel.org>, 
	Andrew Ballance <andrewjballance@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, linux-kernel@...r.kernel.org, 
	maple-tree@...ts.infradead.org, rust-for-linux@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCH v3 1/3] rust: maple_tree: add MapleTree

On Tue, Sep 02, 2025 at 11:01:19AM +0200, Danilo Krummrich wrote:
> On Tue Sep 2, 2025 at 10:35 AM CEST, Alice Ryhl wrote:
> > The maple tree will be used in the Tyr driver to allocate and keep track
> > of GPU allocations created internally (i.e. not by userspace). It will
> > likely also be used in the Nova driver eventually.
> >
> > This adds the simplest methods for additional and removal that do not
> > require any special care with respect to concurrency.
> >
> > This implementation is based on the RFC by Andrew but with significant
> > changes to simplify the implementation.
> >
> > Co-developed-by: Andrew Ballance <andrewjballance@...il.com>
> > Signed-off-by: Andrew Ballance <andrewjballance@...il.com>
> > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> 
> One nit below, otherwise:
> 
> 	Reviewed-by: Danilo Krummrich <dakr@...nel.org>

Thanks!

> > +    pub fn insert_range<R>(&self, range: R, value: T, gfp: Flags) -> Result<(), InsertError<T>>
> > +    where
> > +        R: RangeBounds<usize>,
> > +    {
> > +        let Some((first, last)) = to_maple_range(range) else {
> > +            return Err(InsertError {
> > +                value,
> > +                cause: InsertErrorKind::InvalidRequest,
> > +            });
> > +        };
> > +
> > +        let ptr = T::into_foreign(value);
> > +
> > +        // SAFETY: The tree is valid, and we are passing a pointer to an owned instance of `T`.
> > +        let res = to_result(unsafe {
> > +            bindings::mtree_insert_range(self.tree.get(), first, last, ptr, gfp.as_raw())
> > +        });
> > +
> > +        if let Err(err) = res {
> > +            // SAFETY: As `mtree_insert_range` failed, it is safe to take back ownership.
> > +            let value = unsafe { T::from_foreign(ptr) };
> > +
> > +            let cause = if err == ENOMEM {
> > +                InsertErrorKind::AllocError(kernel::alloc::AllocError)
> > +            } else if err == EEXIST {
> > +                InsertErrorKind::Occupied
> > +            } else {
> > +                InsertErrorKind::InvalidRequest
> > +            };
> > +            Err(InsertError { value, cause })
> > +        } else {
> > +            Ok(())
> > +        }
> > +    }
> 
> 	// SAFETY: The tree is valid, and we are passing a pointer to an owned instance of `T`.
> 	to_result(unsafe {
> 	    bindings::mtree_insert_range(self.tree.get(), first, last, ptr, gfp.as_raw())
> 	}).map_err(|err| {
> 	    // SAFETY: As `mtree_insert_range` failed, it is safe to take back ownership.
> 	    let value = unsafe { T::from_foreign(ptr) };
> 	
> 	    let cause = if err == ENOMEM {
> 	        InsertErrorKind::AllocError(kernel::alloc::AllocError)
> 	    } else if err == EEXIST {
> 	        InsertErrorKind::Occupied
> 	    } else {
> 	        InsertErrorKind::InvalidRequest
> 	    };
> 	    Err(InsertError { value, cause })
> 	})
> 
> I think that's a bit cleaner than the above (not compile tested).

I don't love it. How about a match instead of if/else?

Alice