Re: [Patch v2] mm/huge_memory: add pmd folio to ds_queue in do_huge_zero_wp_pmd()

[Lance Yang <lance.yang@linux.dev>]

On 2025/10/4 10:04, Wei Yang wrote:
> On Fri, Oct 03, 2025 at 09:49:28PM +0800, Lance Yang wrote:
>> Hey Wei,
>>
>> On 2025/10/2 09:38, Wei Yang wrote:
>>> We add pmd folio into ds_queue on the first page fault in
>>> __do_huge_pmd_anonymous_page(), so that we can split it in case of
>>> memory pressure. This should be the same for a pmd folio during wp
>>> page fault.
>>>
>>> Commit 1ced09e0331f ("mm: allocate THP on hugezeropage wp-fault") miss
>>> to add it to ds_queue, which means system may not reclaim enough memory
>>
>> IIRC, it was commit dafff3f4c850 ("mm: split underused THPs") that
>> started unconditionally adding all new anon THPs to _deferred_list :)
>>
> 
> Thanks for taking a look.
> 
> While at this time do_huge_zero_wp_pmd() is not introduced, how it fix a

Ah, I see. I was focused on the policy change ...

> non-exist case? And how could it be backported? I am confused here.

And, yes, 1ced09e0331f ("mm: allocate THP on hugezeropage wp-fault") was
merged later and it introduced the new do_huge_zero_wp_pmd() path without
aligning with the policy ...

Thanks for clarifying!
Lance

> 
>>> in case of memory pressure even the pmd folio is under used.
>>>
>>> Move deferred_split_folio() into map_anon_folio_pmd() to make the pmd
>>> folio installation consistent.
>>>
>>> Fixes: 1ced09e0331f ("mm: allocate THP on hugezeropage wp-fault")
>>
>> Shouldn't this rather be the following?
>>
>> Fixes: dafff3f4c850 ("mm: split underused THPs")
>>
>> Thanks,
>> Lance
>