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.