Re: [PATCH v2] mm: prohibit the last subpage from reusing the entire large folio

[David Hildenbrand <david@redhat.com>]

On 08.03.24 14:45, Ryan Roberts wrote:
> On 08/03/2024 13:24, David Hildenbrand wrote:
>>>>> This patch migrates the last subpage to a small folio and immediately
>>>>> returns the large folio to the system. It benefits both memory availability
>>>>> and anti-fragmentation.
>>>>
>>>> It might be controversial optimization, and as Ryan said, there, are likely
>>>> other cases where we'd want to migrate off-of a thp if possible earlier.
>>>
>>> Personally, I think there might also be cases where you want to copy/reuse the
>>> entire large folio. If you're application is using 16K THPs perhaps it's a
>>> bigger win to just treat it like a base page? I expect the cost/benefit will
>>> change as the THP size increases?
>>
>> Yes, I think for small folios (i.e., 16KiB) it will be rather easy to make a
>> decision. The larger the folio, the larger the page fault latency due to
>> scanning, copying, modifying, which can easily turn undesirable.
>>
>> At least when it comes to page reuse, I have some simple backup plans for small
>> folios if I won't be able to make progress with my other approach.
> 
> Do you mean "small large folios" here? i.e. order >= 1? If so, great!

*smaller*, yes :)

-- 
Cheers,

David / dhildenb