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

[Helge Deller]

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