Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap flags

Kirill A. Shutemov
2017-08-25T16:56:20Z

On Fri, Aug 25, 2017 at 04:19:19PM +0000, Helge Deller 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 */

I guess it's better to re-define MAP_TYPE as 0x3 everywhere and make
MAP_DIRECT a normal flag. It's not new type of mapping anyway.

--
Kirill A. Shutemov