On Wed, Dec 2, 2015 at 2:00 PM, Dave Hansen <[email protected]> wrote: > On 12/02/2015 12:54 PM, Dan Williams wrote: >> On Wed, Dec 2, 2015 at 1:37 PM, Toshi Kani <[email protected]> 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. > > With sparsemem at least, it makes sure that you're looking at a valid > _section_. See the pfn_valid() at ~include/linux/mmzone.h:1222.
At a minimum we would need to add "depends on SPARSEMEM" to "config FS_DAX_PMD". -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
