Messages in this thread | | | From | Dan Williams <> | Date | Thu, 15 Sep 2016 17:16:42 -0700 | Subject | Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs |
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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?
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