Re: [PATCH v2 1/4] mm/migrate: do not migrate folios mapped into VM_LOCKED VMAs under compaction

[Lorenzo Stoakes]

On Tue, Jul 07, 2026 at 02:44:50PM +0100, Lorenzo Stoakes wrote:
> See above about deduplicating.
>
> > +			ttu |= TTU_RESPECT_MLOCK;
>
> Hmm. I don't love 'respect mlock'. I guess we only know about the reason
> being compaction here.
>
> But I'm confused anyway. We have the folio, why aren't we just checking for
> PG_mlocked() here instead of getting the rmap to see if it's mapped
> anywhere with VMA_LOCKED_BIT?

Also, since compaction_allow_unevictable() is a function that is accessible
elsewhere, you could literally just have a TTU_MIGRATION here instead and have
the rmap logic call compaction_allow_unevictable() instead rather than this.

And then you could adapt the function I suggested before not to take a reason
parameter but rather a 'is_migration' one instead possibly and then pass (ttu &
TTU_MIGRATION) in.

BUT. I still question whether this is at all needed since you have the folio you
can check for PG_mlocked...

Cheers, Lorenzo