Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions

[Matthew Wilcox]

On Fri, Dec 14, 2018 at 11:53:31AM -0800, Dave Hansen wrote:
> On 12/14/18 11:48 AM, Matthew Wilcox wrote:
> > I think we can do better than a proxy object with bit 0 set.  I'd go
> > for allocating something like this:
> > 
> > struct dynamic_page {
> > 	struct page;
> > 	unsigned long vaddr;
> > 	unsigned long pfn;
> > 	...
> > };
> > 
> > and use a bit in struct page to indicate that this is a dynamic page.
> 
> That might be fun.  We'd just need a fast/static and slow/dynamic path
> in page_to_pfn()/pfn_to_page().  We'd also need some kind of auxiliary
> pfn-to-page structure since we could not fit that^ structure in vmemmap[].

Yes; working on the pfn-to-page structure right now as it happens ...
in the meantime, an XArray for it probably wouldn't be _too_ bad.