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

[David Hildenbrand]

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