Re: [PATCH v8 1/8] mm: migrate: Allow misplaced migration without VMA

[Davidlohr Bueso]

On Tue, 28 Jul 2026, Bharata B Rao wrote:

> We want isolation of misplaced folios to work in contexts
> where VMA isn't available, typically when performing migrations
> from a kernel thread context. In order to prepare for that,
> allow migrate_misplaced_folio_prepare() to be called with
> a NULL VMA.
>
> When migrate_misplaced_folio_prepare() is called with non-NULL
> VMA, it will check if the folio is mapped shared and that requires
> holding PTL lock. This path isn't taken when the function is
> invoked with NULL VMA (migration outside of process context).
> Therefore, when VMA == NULL, migrate_misplaced_folio_prepare()
> does not require the caller to hold the PTL.
>
> Signed-off-by: Bharata B Rao <bharata@xxxxxxx>

Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>