linux-kernel - Re: [PATCH v6 01/26] rust: alloc: add `Allocator` trait

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Message-ID: <d5761d8e-8e17-42a5-9793-92edb121428e@proton.me>
Date: Tue, 10 Sep 2024 13:03:48 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Danilo Krummrich <dakr@...nel.org>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com, boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com, a.hindborg@...sung.com, aliceryhl@...gle.com, akpm@...ux-foundation.org, daniel.almeida@...labora.com, faith.ekstrand@...labora.com, boris.brezillon@...labora.com, lina@...hilina.net, mcanal@...lia.com, zhiw@...dia.com, cjia@...dia.com, jhubbard@...dia.com, airlied@...hat.com, ajanulgu@...hat.com, lyude@...hat.com, linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v6 01/26] rust: alloc: add `Allocator` trait

On 03.09.24 13:56, Danilo Krummrich wrote:
> On Fri, Aug 30, 2024 at 01:06:00PM +0000, Benno Lossin wrote:
>> On 29.08.24 23:56, Danilo Krummrich wrote:
>>> On Thu, Aug 29, 2024 at 06:19:09PM +0000, Benno Lossin wrote:
>>>> On 16.08.24 02:10, Danilo Krummrich wrote:
>>>>> Add a kernel specific `Allocator` trait, that in contrast to the one in
>>>>> Rust's core library doesn't require unstable features and supports GFP
>>>>> flags.
>>>>>
>>>>> Subsequent patches add the following trait implementors: `Kmalloc`,
>>>>> `Vmalloc` and `KVmalloc`.
>>>>>
>>>>> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
>>>>> Signed-off-by: Danilo Krummrich <dakr@...nel.org>
>>>>
>>>> We discussed this in our weekly meeting (I think ~one week ago?). If you
>>>> give me a draft version of the comment that you plan to add regarding
>>>> the `old_layout` parameter, I can see if I am happy with it. If I am, I
>>>> would give you my RB.
>>>
>>> May I propose you let me know what you would like to see covered, rather than
>>> me trying to guess it. :-)
>>
>> I was hoping that we put that in our meeting notes, but I failed to find
>> them... I would put this in a normal comment, so it doesn't show up in the
>> documentation. Preface it like implementation decision/detail:
>> - Why do `Allocator::{realloc,free}` not have an `old_layout` parameter
>>   like in the stdlib? (the reasons you had for that decision, like we
>>   don't need it etc.)
> 
> Ok.
> 
>> - Then something along the lines of "Note that no technical reason is
>>   listed above, so if you need/want to implement an allocator taking
>>   advantage of that, you can change it"
> 
> I don't really want to set the conditions for this to change in the
> documentation. It really depends on whether it's actually needed or the
> advantage of having it is huge enough to leave the core kernel allocators with
> unused arguments.
> 
> This can really only be properly evaluated case by case in a discussion.

Agreed, but I don't want people to think that we have a reason against
doing it in the future. Do you have an idea how to convey this?

---
Cheers,
Benno