Re: [PATCH v3 3/7] rust: alloc: implement VmallocPageIter

["Danilo Krummrich" <dakr@kernel.org>]

On Mon Aug 11, 2025 at 11:14 AM CEST, Alice Ryhl wrote:
> On Fri, Aug 08, 2025 at 08:10:17PM +0200, Danilo Krummrich wrote:
>> +/// An [`Iterator`] of [`page::BorrowedPage`] items owned by a [`Vmalloc`] allocation.
>> +///
>> +/// # Guarantees
>> +///
>> +/// The pages iterated by the [`Iterator`] appear in the order as they are mapped in the CPU's
>> +/// virtual address space ascendingly.
>> +///
>> +/// # Invariants
>> +///
>> +/// - `buf` is a valid pointer to the beginning of a [`Vmalloc`] allocation.
>> +/// - `size` is the size of the [`Vmalloc`] allocation `buf` points to.
>> +pub struct VmallocPageIter<'a> {
>> +    /// The base address of the [`Vmalloc`] buffer.
>> +    buf: NonNull<u8>,
>> +    /// The size of the buffer pointed to by `buf` in bytes.
>> +    size: usize,
>> +    /// The current page index of the [`Iterator`].
>> +    index: usize,
>
> My understanding is that an implementation using two pointers that
> repeatedly increments the starting pointer until it reaches the end
> pointer is more efficient.

If I directly advance the start pointer until hitting the end pointer, I need
three pointers, i.e. start, end and the advancing one, otherwise I can't
implement base_address() anymore, hence I went with an index instead.