From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@lst.de>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Nicholas Piggin <npiggin@gmail.com>,
XFS Developers <xfs@oss.sgi.com>, Linux MM <linux-mm@kvack.org>,
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 10:09:42 -0700 [thread overview]
Message-ID: <20160915170942.GJ9314@birch.djwong.org> (raw)
In-Reply-To: <CAPcyv4jTw3cXpmmJRh7t16Xy2uYofDe+fJ+X_jnz+Q=o0uGneg@mail.gmail.com>
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?
Seeing as FS_IOC_FSGETXATTR is a "generic" ioctl now, why not just
implement it for all the DAX fses and block devices? Aside from xflags,
the other fields are probably all zero for non-xfs (aside from project
quota id I guess).
(Yeah, sort of awkward, I know...)
--D
> The other problem with hiding the DAX property is that it turns out to
> not be a transparent acceleration feature. See xfs/086 xfs/088
> xfs/089 xfs/091 which fail with DAX and, as far as I understand, it is
> due to the fact that DAX disallows delayed allocation behavior.
>
> If behavior changes I think we should indicate that to userspace and
> VM_DAX is certainly more useful to userspace than some of the other vm
> internals we already export in those flags.
>
> _______________________________________________
> xfs mailing list
> xfs@oss.sgi.com
> http://oss.sgi.com/mailman/listinfo/xfs
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next prev parent reply other threads:[~2016-09-15 17:09 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 [this message]
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
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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