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

[Davidlohr Bueso <dave@stgolabs.net>]

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@amd.com>

Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>