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

[Jason Gunthorpe]

On Sat, Aug 17, 2019 at 01:31:28PM +0200, Christoph Hellwig wrote:
> 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.

Oh, yes, that was far too hasty on my part, I had assumed collect set
the cpages. Thank you for checking

Jason