On Wed, 2015-12-02 at 12:54 -0800, Dan Williams wrote: > On Wed, Dec 2, 2015 at 1:37 PM, Toshi Kani <toshi.kani@xxxxxxx> 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. I believe we use the version of pfn_valid() in linux/mmzone.h. Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>