Re: [PATCH] mm/migrate_device: remove dead migration entry check in migrate_vma_collect_huge_pmd()

[Alistair Popple <apopple@nvidia.com>]

On 2026-02-12 at 12:46 +1100, Davidlohr Bueso <dave@stgolabs.net> wrote...
> The softleaf_is_migration() check is unreachable as entries that are not
> device_private are filtered out. Similarly, the PTE-level equivalent in
> migrate_vma_collect_pmd() skips migration entries.
> 
> This dead branch also contained a double spin_unlock(ptl) bug.

Heh. You beat me by 10 minutes :-) I was just checking to see if the fix had
already been sent before pressing send on mine.

You probably want to add:

Fixes: a30b48bf1b244 ("mm/migrate_device: implement THP migration of zone device pages")

But other than that this looks good so:

Reviewed-by: Alistair Popple <apopple@nvidia.com>

> Suggested-by: Matthew Brost <matthew.brost@intel.com>
> Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
> ---
>  mm/migrate_device.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
> index c2855235fd9a..b40c1d49677d 100644
> --- a/mm/migrate_device.c
> +++ b/mm/migrate_device.c
> @@ -175,13 +175,6 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start,
>  			return migrate_vma_collect_skip(start, end, walk);
>  		}
>  
> -		if (softleaf_is_migration(entry)) {
> -			migration_entry_wait_on_locked(entry, ptl);
> -			spin_unlock(ptl);
> -			return -EAGAIN;
> -		}
> -
>  		if (softleaf_is_device_private_write(entry))
>  			write = MIGRATE_PFN_WRITE;
>  	} else {
> --
> 2.39.5
> 
>