Re: [v2 PATCH 3/7] mm: thp: refactor NUMA fault handling

[Yang Shi]

On Mon, May 17, 2021 at 8:27 AM Mel Gorman <mgorman@xxxxxxx> wrote:
>
> On Tue, Apr 13, 2021 at 02:24:12PM -0700, Yang Shi wrote:
> > When the THP NUMA fault support was added THP migration was not supported yet.
> > So the ad hoc THP migration was implemented in NUMA fault handling.  Since v4.14
> > THP migration has been supported so it doesn't make too much sense to still keep
> > another THP migration implementation rather than using the generic migration
> > code.
> >
> > This patch reworked the NUMA fault handling to use generic migration implementation
> > to migrate misplaced page.  There is no functional change.
> >
> > After the refactor the flow of NUMA fault handling looks just like its
> > PTE counterpart:
> >   Acquire ptl
> >   Prepare for migration (elevate page refcount)
> >   Release ptl
> >   Isolate page from lru and elevate page refcount
> >   Migrate the misplaced THP
> >
> > If migration is failed just restore the old normal PMD.
> >
> > In the old code anon_vma lock was needed to serialize THP migration
> > against THP split, but since then the THP code has been reworked a lot,
> > it seems anon_vma lock is not required anymore to avoid the race.
> >
> > The page refcount elevation when holding ptl should prevent from THP
> > split.
> >
> > Use migrate_misplaced_page() for both base page and THP NUMA hinting
> > fault and remove all the dead and duplicate code.
> >
> > Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
>
> I did not spot any big problems and FWIW, the series overall passed a
> series of tests that exercise NUMA balancing migrations so...
>
> Acked-by: Mel Gorman <mgorman@xxxxxxx>

Thanks a lot for testing and reviewing the series.

>
> --
> Mel Gorman
> SUSE Labs