On Fri, Aug 25, 2017 at 9:19 AM, Helge Deller <deller@xxxxxx> wrote: > On 25.08.2017 18:16, Kirill A. Shutemov wrote: >> On Fri, Aug 25, 2017 at 09:02:36AM -0700, Christoph Hellwig wrote: >>> On Fri, Aug 25, 2017 at 06:58:03PM +0300, Kirill A. Shutemov wrote: >>>> Not all archs are ready for this: >>>> >>>> arch/parisc/include/uapi/asm/mman.h:#define MAP_TYPE 0x03 /* Mask for type of mapping */ >>>> arch/parisc/include/uapi/asm/mman.h:#define MAP_FIXED 0x04 /* Interpret addr exactly */ >>> >>> I'd be happy to say that we should not care about parisc for >>> persistent memory. We'll just have to find a way to exclude >>> parisc without making life too ugly. >> >> I don't think creapling mmap() interface for one arch is the right way to >> go. I think the interface should be universal. >> >> I may imagine MAP_DIRECT can be useful not only for persistent memory. >> For tmpfs instead of mlock()? > > On parisc we have > #define MAP_SHARED 0x01 /* Share changes */ > #define MAP_PRIVATE 0x02 /* Changes are private */ > #define MAP_TYPE 0x03 /* Mask for type of mapping */ > #define MAP_FIXED 0x04 /* Interpret addr exactly */ > #define MAP_ANONYMOUS 0x10 /* don't use a file */ > > So, if you need a MAP_DIRECT, wouldn't e.g. > #define MAP_DIRECT 0x08 > be possible (for parisc, and others 0x04). > And if MAP_TYPE needs to include this flag on parisc: > #define MAP_TYPE (0x03 | 0x08) /* Mask for type of mapping */ The problem here is that to support new the mmap flags the arch needs to find a flag that is guaranteed to fail on older kernels. Defining MAP_DIRECT to 0x8 on parisc doesn't work because it will simply be ignored on older parisc kernels. However, it's already the case that several archs have their own sys_mmap entry points. Those archs that can't follow the common scheme (only parsic it seems) will need to add a new mmap syscall. I think that's a reasonable tradeoff to allow every other architecture to add this support with their existing mmap syscall paths. That means MAP_DIRECT should be defined to MAP_TYPE on parisc until it later defines an opt-in mechanism to a new syscall that honors MAP_DIRECT as a valid flag.
