Re: [PATCH 1/4] migrate: Allow migrate_misplaced_folio APIs without a VMA

Gregory Price
2024-12-02T15:48:59Z

On Thu, Nov 28, 2024 at 07:12:11PM +0800, Huang, Ying wrote:
> Hi, Gregory,
>
> Gregory Price <gourry@gourry.net> writes:
>
> > To migrate unmapped pagecache folios, migrate_misplaced_folio and
> > migrate_misplaced_folio_prepare must handle folios without VMAs.
>
> IMHO, it's better to use migrate_misplaced_folio() instead of
> migrate_misplaced_folio for readability in patch title and description.
>
> > migrate_misplaced_folio_prepare checks VMA for exec bits, so allow
> > a NULL VMA when it does not have a mapping.
> >
> > migrate_misplaced_folio must call migrate_pages with MIGRATE_SYNC
> > when in the pagecache path because it is a synchronous context.
>
> I don't find the corresponding implementation for this. And, I don't
> think it's a good idea to change from MIGRATE_ASYNC to MIGRATE_SYNC.
> This may cause too long page access latency for page placement
> optimization. The downside may offset the benefit.
>
> And, it appears that we can delete the "vma" parameter of
> migrate_misplaced_folio() because it's not used now. This is a trivial
> code cleanup.
>

This patch apparently got a bit away from me and was heavily reduced
from its initial form. This commit message is just wrong now. I will
update this and the 2nd commit and probably submit them separately.

~Gregory