On Mon, Nov 23, 2020 at 11:42:58AM +0100, Michal Hocko wrote: > On Mon 23-11-20 18:36:33, Muchun Song wrote: > > > No I really mean that pfn_to_page will give you a struct page pointer > > > from pages which you release from the vmemmap page tables. Those pages > > > might get reused as soon sa they are freed to the page allocator. > > > > We will remap vmemmap pages 2-7 (virtual addresses) to page > > frame 1. And then we free page frame 2-7 to the buddy allocator. > > And this doesn't really happen in an atomic fashion from the pfn walker > POV, right? So it is very well possible that > > struct page *page = pfn_to_page(); > // remapping happens here > // page content is no longer valid because its backing memory can be > // reused for whatever purpose.
pfn_to_page() returns you a virtual address. That virtual address remains a valid pointer to exactly the same contents, it's just that the page tables change to point to a different struct page which has the same compound_head().
