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

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Date:   Fri, 25 Aug 2017 19:56:12 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Helge Deller <deller@....de>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, Arnd Bergmann <arnd@...db.de>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Linux API <linux-api@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-xfs@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
        Andy Lutomirski <luto@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-parisc@...r.kernel.org
Subject: Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap
 flags

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