Re: [PATCH 01/10] mm: turn migrate_vma upside down

[Christoph Hellwig]

On Fri, Aug 16, 2019 at 05:11:07PM +0000, Jason Gunthorpe wrote:
> -     if (args->cpages)
> -             migrate_vma_prepare(args);
> -     if (args->cpages)
> -             migrate_vma_unmap(args);
> +     if (!args->cpages)
> +             return 0;
> +
> +     migrate_vma_prepare(args);
> +     migrate_vma_unmap(args);

I don't think this is ok.  Both migrate_vma_prepare and migrate_vma_unmap
can reduce args->cpages, including possibly to 0.