Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device_page() with a single reference

[Kirill A. Shutemov]

On Fri, Apr 28, 2017 at 03:33:07PM -0400, Jerome Glisse wrote:
> On Fri, Apr 28, 2017 at 12:22:24PM -0700, Dan Williams wrote:
> > Are you sure about needing to hook the 2 -> 1 transition? Could we
> > change ZONE_DEVICE pages to not have an elevated reference count when
> > they are created so you can keep the HMM references out of the mm hot
> > path?
> 
> 100% sure on that :) I need to callback into driver for 2->1 transition
> no way around that. If we change ZONE_DEVICE to not have an elevated
> reference count that you need to make a lot more change to mm so that
> ZONE_DEVICE is never use as fallback for memory allocation. Also need
> to make change to be sure that ZONE_DEVICE page never endup in one of
> the path that try to put them back on lru. There is a lot of place that
> would need to be updated and it would be highly intrusive and add a
> lot of special cases to other hot code path.

Could you explain more on where the requirement comes from or point me to
where I can read about this.

-- 
 Kirill A. Shutemov