Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs
Date	2016-09-16 02:20 +0200
Message-ID	<shP2N-5Du-5@gated-at.bofh.it> (permalink)
References	<shyOl-3Aa-5@gated-at.bofh.it> <shyOm-3Aa-17@gated-at.bofh.it> <shAds-4BB-21@gated-at.bofh.it> <shIkF-1p0-1@gated-at.bofh.it> <shNX4-4Wt-21@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Thu, Sep 15, 2016 at 4:07 PM, Dave Chinner <david@fromorbit.com> wrote:
> On Thu, Sep 15, 2016 at 10:01:03AM -0700, Dan Williams wrote:
>> On Thu, Sep 15, 2016 at 1:26 AM, Christoph Hellwig <hch@lst.de> wrote:
>> > On Wed, Sep 14, 2016 at 11:54:38PM -0700, Dan Williams wrote:
>> >> The DAX property, page cache bypass, of a VMA is only detectable via the
>> >> vma_is_dax() helper to check the S_DAX inode flag.  However, this is
>> >> only available internal to the kernel and is a property that userspace
>> >> applications would like to interrogate.
>> >
>> > They have absolutely no business knowing such an implementation detail.
>>
>> Hasn't that train already left the station with FS_XFLAG_DAX?
>
> No, that's an admin flag, not a runtime hint for applications. Just
> because that flag is set on an inode, it does not mean that DAX is
> actually in use - it will be ignored if the backing dev is not dax
> capable.
>

What's the point of an admin flag if an admin can't do cat /proc/<pid
of interest>/smaps, or some other mechanism, to validate that the
setting the admin cares about is in effect?

Thread

[PATCH v2 0/3] mm,  dax: export dax capabilities and mapping size info to userspace Dan Williams <dan.j.williams@intel.com> - 2016-09-15 09:00 +0200
  [PATCH v2 1/3] mm, dax: add VM_SYNC flag for device-dax VMAs Dan Williams <dan.j.williams@intel.com> - 2016-09-15 09:00 +0200
  [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dan Williams <dan.j.williams@intel.com> - 2016-09-15 09:00 +0200
    Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Christoph Hellwig <hch@lst.de> - 2016-09-15 10:30 +0200
      Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dan Williams <dan.j.williams@intel.com> - 2016-09-15 19:10 +0200
        Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs "Darrick J. Wong" <darrick.wong@oracle.com> - 2016-09-15 19:20 +0200
          Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dan Williams <dan.j.williams@intel.com> - 2016-09-15 19:50 +0200
        Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dave Chinner <david@fromorbit.com> - 2016-09-16 01:10 +0200
          Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dan Williams <dan.j.williams@intel.com> - 2016-09-16 01:20 +0200
          Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dan Williams <dan.j.williams@intel.com> - 2016-09-16 02:20 +0200
            Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dave Chinner <david@fromorbit.com> - 2016-09-16 03:30 +0200
              Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dan Williams <dan.j.williams@intel.com> - 2016-09-16 04:10 +0200
                Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dan Williams <dan.j.williams@intel.com> - 2016-09-16 05:50 +0200
                Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dave Chinner <david@fromorbit.com> - 2016-09-16 07:40 +0200
                Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dan Williams <dan.j.williams@intel.com> - 2016-09-16 12:50 +0200

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