From: Dan Williams <dan.j.williams@intel.com>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@lst.de>, Linux MM <linux-mm@kvack.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Nicholas Piggin <npiggin@gmail.com>,
XFS Developers <xfs@oss.sgi.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs
Date: Thu, 15 Sep 2016 17:16:42 -0700 [thread overview]
Message-ID: <CAPcyv4jvcWEc2TkRh6-MoKb_-1VbFoiKUJEB=svQO+BVN8s-Sg@mail.gmail.com> (raw)
In-Reply-To: <20160915230748.GS30497@dastard>
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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next prev parent reply other threads:[~2016-09-16 0:16 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-15 6:54 [PATCH v2 0/3] mm, dax: export dax capabilities and mapping size info to userspace Dan Williams
2016-09-15 6:54 ` [PATCH v2 1/3] mm, dax: add VM_SYNC flag for device-dax VMAs Dan Williams
2016-09-15 6:54 ` [PATCH v2 2/3] mm, dax: add VM_DAX flag for DAX VMAs Dan Williams
2016-09-15 8:26 ` Christoph Hellwig
2016-09-15 17:01 ` Dan Williams
2016-09-15 17:09 ` Darrick J. Wong
2016-09-15 17:44 ` Dan Williams
2016-09-15 23:07 ` Dave Chinner
2016-09-15 23:19 ` Dan Williams
2016-09-16 0:16 ` Dan Williams [this message]
2016-09-16 1:24 ` Dave Chinner
2016-09-16 2:04 ` Dan Williams
2016-09-16 3:41 ` Dan Williams
2016-09-16 5:36 ` Dave Chinner
2016-09-16 10:47 ` Dan Williams
2016-09-15 6:54 ` [PATCH v2 3/3] mm, mincore2(): retrieve tlb-size attributes of an address range Dan Williams
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