Messages in this thread | | | Date | Wed, 2 Dec 2015 12:54:05 -0800 | Subject | Re: [PATCH] mm: Fix mmap MAP_POPULATE for DAX pmd mapping | From | Dan Williams <> |
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On Wed, Dec 2, 2015 at 1:37 PM, Toshi Kani <toshi.kani@hpe.com> wrote: > On Wed, 2015-12-02 at 11:57 -0800, Dan Williams wrote: [..] >> The whole point of __get_user_page_fast() is to avoid the overhead of >> taking the mm semaphore to access the vma. _PAGE_SPECIAL simply tells >> __get_user_pages_fast that it needs to fallback to the >> __get_user_pages slow path. > > I see. Then, I think gup_huge_pmd() can simply return 0 when !pfn_valid(), > instead of VM_BUG_ON.
Is pfn_valid() a reliable check? It seems to be based on a max_pfn per node... what happens when pmem is located below that point. I haven't been able to convince myself that we won't get false positives, but maybe I'm missing something.
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