Re: [PATCH RFC v3 01/19] mm: thread user_addr through page allocator for cache-friendly zeroing

[David Hildenbrand (Arm)]

On 4/24/26 20:41, Matthew Wilcox wrote:
> On Tue, Apr 21, 2026 at 06:01:10PM -0400, Michael S. Tsirkin wrote:
>> Thread a user virtual address from vma_alloc_folio() down through
>> the page allocator to post_alloc_hook().  This is plumbing preparation
>> for a subsequent patch that will use user_addr to call folio_zero_user()
>> for cache-friendly zeroing of user pages.
>>
>> The user_addr is stored in struct alloc_context and flows through:
>>   vma_alloc_folio -> folio_alloc_mpol -> __alloc_pages_mpol ->
>>   __alloc_frozen_pages -> get_page_from_freelist -> prep_new_page ->
>>   post_alloc_hook
> 
> I don't like this.  I think we should instead lift the zeroing from
> post_alloc_hook() to the callers of __alloc_frozen_pages().

I don't think so. In particular how zeroing optimizations are related to buddy
details (tag zeroing, kasan unpoisoning, init_on_alloc/init_on_free, now
pre-zeroing).

> 
> I don't understand why you want to remove the double-zeroing of memory
> when the user has asked for zero_on_alloc.  They asked for stupid things,
> let them bear the cost.

That's not how the world works :)


-- 
Cheers,

David