linux-kernel - Re: [PATCH 1/2] xfs: always use DAX if mount option is used

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Message-ID: <20170908152805.GA16646@linux.intel.com>
Date:   Fri, 8 Sep 2017 09:28:05 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-nvdimm@...ts.01.org, Dave Chinner <david@...morbit.com>,
        stable@...r.kernel.org, Christoph Hellwig <hch@....de>,
        linux-xfs@...r.kernel.org
Subject: Re: [PATCH 1/2] xfs: always use DAX if mount option is used

On Fri, Sep 08, 2017 at 12:20:28AM -0700, Christoph Hellwig wrote:
> On Thu, Sep 07, 2017 at 03:08:31PM -0600, Ross Zwisler wrote:
> > Before support for the per-inode DAX flag was disabled the XFS the code had
> > an issue where the user couldn't reliably tell whether or not DAX was being
> > used to service page faults and I/O when the DAX mount option was used.  In
> > this case each inode within the mounted filesystem started with S_DAX set
> > due to the mount option, but it could be cleared if someone touched the
> > individual inode flag.
> 
> Looks good, but can you please add a testcase to xfstests for this?

Hmm...aside from looking at tracepoints, I'm not sure how to detect whether or
not S_DAX is actually being used for an inode.  I don't see any other xfstests
that try and look at the trace buffer, but I guess that could work.

Do you know of a better way to detect this test failure/success?

> Reviewed-by: Christoph Hellwig <hch@....de>

Thanks for the review!