[PATCH v6 08/13] mm: call pgmap->ops->page_free for DEVICE_GENERIC pages

[Christoph Hellwig]

On Mon, Aug 16, 2021 at 03:00:49PM -0400, Felix Kuehling wrote:
> 
> Am 2021-08-15 um 11:40 a.m. schrieb Christoph Hellwig:
> > On Fri, Aug 13, 2021 at 01:31:45AM -0500, Alex Sierra wrote:
> >> Add MEMORY_DEVICE_GENERIC case to free_zone_device_page callback.
> >> Device generic type memory case is now able to free its pages properly.
> > How is this going to work for the two existing MEMORY_DEVICE_GENERIC
> > that now change behavior?  And which don't have a ->page_free callback
> > at all?
> 
> That's a good catch. Existing drivers shouldn't need a page_free
> callback if they didn't have one before. That means we need to add a
> NULL-pointer check in free_device_page.

Also the other state clearing (__ClearPageWaiters/mem_cgroup_uncharge/
->mapping = NULL).

In many ways this seems like you want to bring back the DEVICE_PUBLIC
pgmap type that was removed a while ago due to the lack of users
instead of overloading the generic type.