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

Helge Deller
2017-08-25T16:20:15Z

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 */

Helge