Re: [PATCH v2 1/1] mm: skip mlocked THPs that are underused early in deferred_split_scan()

David Hildenbrand
2025-09-08T11:32:14Z

On 08.09.25 12:38, Kiryl Shutsemau wrote:
> On Mon, Sep 08, 2025 at 05:07:41PM +0800, Lance Yang wrote:
>> From: Lance Yang <lance.yang@linux.dev>
>>
>> When we stumble over a fully-mapped mlocked THP in the deferred shrinker,
>> it does not make sense to try to detect whether it is underused, because
>> try_to_map_unused_to_zeropage(), called while splitting the folio, will not
>> actually replace any zeroed pages by the shared zeropage.
>
> It makes me think, does KSM follows the same logic as
> try_to_map_unused_to_zeropage()?
>
> I cannot immediately find what prevents KSM from replacing zeroed mlocked
> folio with ZERO_PAGE().
>
> Hm?

I assume if you're using mlock and at the same time enable KSM for a
process/VMA, you're doing something wrong.

In contrast, THP is supposed to be transparent (yeah, I know ...).

--
Cheers

David / dhildenb