Re: [PATCH v10 07/37] mm: thread user_addr through page allocator for cache-friendly zeroing

["David Hildenbrand (Arm)" <david@kernel.org>]

On 6/8/26 17:27, Zi Yan wrote:
> On 8 Jun 2026, at 7:08, David Hildenbrand (Arm) wrote:
> 
>> On 6/8/26 12:23, Lorenzo Stoakes wrote:
>>> I noticed this patch, again, sneaks in some additional code changes that
>>> are not mentioned in the commit message and seem irrelevant to the patch.
>>>
>>> Not sure if the AI is doing this, but please don't do that.
>>>
>>>
>>> This feels like very weak justification for code that massively changes mm
>>> code and makes it all much worse.
>>>
>>>
>>> Is this the only relevant code path? You're changing a TON of code here
>>> that will have multiple different code paths?
>>>
>>>
>>> Ugh god, so now we're passing a user address through allocation paths that
>>> might not even be aware of this or be allocating memory at a point when the
>>> mapping is known?
>>
>> The original ideas was to do this only with internal interfaces. I think I
>> raised before to leave hugetlb alone for now.
>>
>> Fundamentally, user_alloc_needs_zeroing() is something we should get rid of, to
>> just be able use __GFP_ZERO and do zeroing at exactly one place.
> 
> Just a reminder that user_alloc_needs_zeroing() not only checks init_on_alloc,
> but also some arc clearing page requirements. To do zeroing in one place,
> clear_page() used in post_alloc_hook() will need to learn how to handle
> arch-specific zeroing from clear_user_page()/clear_user_highpage().

Right.

> 
>>
>>
>> The question is how to pass that information (user_addr) through internal APIs.
> 
> Or should we defer zeroing after a page is returned from allocator? So that
> user_addr does not need to be passed through irrelevant allocation APIs.
> Something like:
> 
> alloc_page_wrapper(gfp, order, user_addr)
> {
> 	page = alloc_pages();
> 	if (gfp & __GFP_ZERO)
> 		clear_page(page);
> }
> 

Not really sure what's best here. I think we'd want to limit the lifting to some
internal API, so it cannot easily be messed up by random kernel code calling
into the wrong API and not getting pages cleared.

-- 
Cheers,

David