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Subject: Re: [PATCH 1/2] mm: introduce put_user_page*(), placeholder versions
To: Matthew Wilcox <willy@infradead.org>,
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From: Dave Hansen <dave.hansen@intel.com>
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Date: Fri, 14 Dec 2018 11:53:31 -0800
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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[].