linux-kernel - Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG

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Date:   Tue, 26 Jun 2018 21:31:01 +0000
From:   "Kani, Toshi" <toshi.kani@....com>
To:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>
Subject: Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG_DAX for fsdax mode

On Tue, 2018-06-26 at 14:28 -0700, Dan Williams wrote:
> On Tue, Jun 26, 2018 at 2:23 PM, Kani, Toshi <toshi.kani@....com> wrote:
> > On Tue, 2018-06-26 at 14:02 -0700, Dan Williams wrote:
> > > On Tue, Jun 26, 2018 at 1:54 PM, Kani, Toshi <toshi.kani@....com> wrote:
> 
> [..]
> > > > When this dm change was made, the pmem driver supported DAX for both raw
> > > > and memory modes (note: sector mode does not use the pmem driver).  I
> > > > think the issue was introduced when we dropped DAX support from raw
> > > > mode.
> > > 
> > > Still DAX with raw mode never really worked any way. It was also
> > > something that was broken from day one. So what happens to someone who
> > > happened to avoid all the problems with page-less DAX and enabled
> > > device-mapper on top? That failure mode detail needs to be added to
> > > this changelog if we want to propose this for -stable.
> > 
> > My point is that the behavior should be consistent between pmem and
> > device-mapper.  When -o dax succeeds on a pmem, then it should succeed
> > on a device-mapper on top of that pmem.
> > 
> > Has the drop of dax support from raw mode made to -stable back to the
> > baseline accepted 545ed20e6df6?  It will introduce inconsistency,
> > otherwise.
> 
> That commit, 569d0365f571 "dax: require 'struct page' by default for
> filesystem dax", has not been tagged for -stable.

Then, Fixes tag should be set to 569d0365f571 to keep the behavior
consistent.

-Toshi