Re: [RFC PATCH 0/9] introduce PGTY_mgt_entry page_type

[David Hildenbrand <david@redhat.com>]

On 24.07.25 11:09, Huan Yang wrote:
> 
> 在 2025/7/24 16:59, David Hildenbrand 写道:
>> On 24.07.25 10:44, Huan Yang wrote:
>>> Summary
>>> ==
>>> This patchset reuses page_type to store migrate entry count during the
>>> period from migrate entry setup to removal, enabling accelerated VMA
>>> traversal when removing migrate entries, following a similar 
>>> principle to
>>> early termination when folio is unmapped in try_to_migrate.
>>
>> I absolutely detest (ab)using page types for that, so no from my side 
>> unless I am missing something important.
>>
>>>
>>> In my self-constructed test scenario, the migration time can be reduced
>>
>> How relevant is that in practice?
> 
> IMO, any folio mapped < nr vma in mapping(anon_vma, addresss_space), 
> will benefit from this.
> 
> So, all pages that have been COW-ed by child processes can be skipped.

For small anon folios, you could use the anon-exclusive marker to derive 
"there can only be a single mapping".

It's stored alongside the migration entry.

So once you restored that single migration entry, you can just stop the 
walk.

-- 
Cheers,

David / dhildenb