From: Dan Williams <dan.j.williams@intel.com>
To: Helge Deller <deller@gmx.de>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
Christoph Hellwig <hch@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jan Kara <jack@suse.cz>, Arnd Bergmann <arnd@arndb.de>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
Linux API <linux-api@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-xfs@vger.kernel.org, Linux MM <linux-mm@kvack.org>,
Andy Lutomirski <luto@kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-parisc@vger.kernel.org
Subject: Re: [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap flags
Date: Fri, 25 Aug 2017 13:24:31 -0700 [thread overview]
Message-ID: <CAPcyv4jeZc8P+E0aHNChzy-wfNpOx3GehKck1nXqJ1b9JdydFA@mail.gmail.com> (raw)
In-Reply-To: <4de21e8d-5e10-ec40-c731-0c079953cf48@gmx.de>
On Fri, Aug 25, 2017 at 9:19 AM, Helge Deller <deller@gmx.de> 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.
--
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next prev parent reply other threads:[~2017-08-25 20:24 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-23 23:48 [PATCH v6 0/5] MAP_DIRECT and block-map-atomic files Dan Williams
[not found] ` <150353211413.5039.5228914877418362329.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-23 23:48 ` [PATCH v6 1/5] vfs: add flags parameter to ->mmap() in 'struct file_operations' Dan Williams
[not found] ` <150353211985.5039.4333061601382775843.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-24 16:58 ` Christoph Hellwig
2017-08-24 17:42 ` Dan Williams
2017-08-23 23:48 ` [PATCH v6 2/5] fs, xfs: introduce S_IOMAP_SEALED Dan Williams
[not found] ` <150353212577.5039.14069456126848863439.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-24 16:13 ` Christoph Hellwig
2017-08-25 6:00 ` Dan Williams
2017-08-25 19:44 ` Dan Williams
2017-08-23 23:48 ` [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating block-map-atomic file ranges Dan Williams
[not found] ` <150353213655.5039.7662200155640827407.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-24 16:11 ` Christoph Hellwig
[not found] ` <20170824161152.GB27591-jcswGhMUV9g@public.gmane.org>
2017-08-24 16:31 ` Dan Williams
2017-08-24 16:39 ` Christoph Hellwig
[not found] ` <20170824163925.GA28503-jcswGhMUV9g@public.gmane.org>
2017-08-24 20:26 ` Dan Williams
2017-08-23 23:49 ` [PATCH v6 5/5] fs, fcntl: add F_MAP_DIRECT Dan Williams
2017-08-23 23:48 ` [PATCH v6 3/5] mm: introduce mmap3 for safely defining new mmap flags Dan Williams
[not found] ` <150353213097.5039.6729469069608762658.stgit-p8uTFz9XbKj2zm6wflaqv1nYeNYlB/vhral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-08-24 13:04 ` Jan Kara
2017-08-24 16:55 ` Christoph Hellwig
[not found] ` <20170824165546.GA3121-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-08-24 17:36 ` Dan Williams
[not found] ` <CAPcyv4iN0QpUSgOUvisnNQsiV1Pp=4dh7CwAV8FFj=_rFU=aug-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-25 13:00 ` Christoph Hellwig
2017-08-25 15:58 ` Kirill A. Shutemov
2017-08-25 16:02 ` Christoph Hellwig
2017-08-25 16:16 ` Kirill A. Shutemov
[not found] ` <20170825161607.6v6beg4zjktllt2z-sVvlyX1904swdBt8bTSxpkEMvNT87kid@public.gmane.org>
2017-08-25 16:19 ` Helge Deller
2017-08-25 16:56 ` Kirill A. Shutemov
2017-08-25 20:24 ` Dan Williams [this message]
[not found] ` <CAPcyv4jeZc8P+E0aHNChzy-wfNpOx3GehKck1nXqJ1b9JdydFA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-26 7:40 ` Helge Deller
2017-08-26 15:15 ` Dan Williams
[not found] ` <CAPcyv4ic0zxQzWEipZ=1LpDC8VnmphGzVSYmrFcjOAgX7esfUw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-26 19:50 ` Helge Deller
2017-08-26 22:46 ` Dan Williams
2017-08-26 23:56 ` Kirill A. Shutemov
2017-08-24 16:08 ` [PATCH v6 0/5] MAP_DIRECT and block-map-atomic files Christoph Hellwig
2017-08-24 16:25 ` Dan Williams
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