From: Ross Zwisler <ross.zwisler@linux.intel.com>
To: "Kani, Toshi" <toshi.kani@hpe.com>
Cc: "dan.j.williams@intel.com" <dan.j.williams@intel.com>,
"ross.zwisler@linux.intel.com" <ross.zwisler@linux.intel.com>,
"dm-devel@redhat.com" <dm-devel@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
"snitzer@redhat.com" <snitzer@redhat.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG_DAX for fsdax mode
Date: Thu, 28 Jun 2018 13:04:24 -0600 [thread overview]
Message-ID: <20180628190424.GC17758@linux.intel.com> (raw)
In-Reply-To: <1530207635.14039.308.camel@hpe.com>
On Thu, Jun 28, 2018 at 05:42:34PM +0000, Kani, Toshi wrote:
> On Tue, 2018-06-26 at 16:04 -0600, Ross Zwisler wrote:
> > On Tue, Jun 26, 2018 at 02:51:52PM -0700, Dan Williams wrote:
> > > On Tue, Jun 26, 2018 at 2:31 PM, Kani, Toshi <toshi.kani@hpe.com> wrote:
> > > > 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@hpe.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@hpe.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.
> > >
> > > Sure, and the failure mode is...? I'm thinking the commit log should say:
> > >
> > > "Starting with commit 569d0365f571 "dax: require 'struct page' by
> > > default for filesystem dax", dax is no longer supported for page-less
> > > configurations. However, device-mapper sees the QUEUE_FLAG_DAX still
> > > being set and falsely assumes that DAX is enabled, this leads to
> > > <insert user visible failure mode details here>"
> >
> > Dan is correct that there is no user visible change for this. It is the right
> > thing to do for consistency and sanity, but it doesn't actually have user
> > visible behavior that needs to be backported to stable.
> >
> > Toshi is correct that this change is only for raw mode namespaces, not btt
> > namespaces.
> >
> > I'll adjust the changelog and remove the stable flag for v5, and I'll add a
> > Fixes: tag for patch 2.
>
> Hi Ross,
>
> Your patches look good. But I am still not clear about the Fixes &
> stable handling. Talking about user visible behavior, I do not think we
> had any issue until dax support was dropped from raw mode. Until then,
> the pmem driver supported dax for all modes, and the check for
> direct_access worked.
I agree that the fsdax + raw mode failure mode I mentioned in my cover letter
only started when we restricted filesystem DAX to having struct page, but I
think that the other failure mode, fsdax + some random block driver (I used
brd) was present in DM from the beginning.
In any case, I think both are fixed with the patches, and I think it's fine
that all 3 get thrown at stable. Thanks, Mike, for the help.
next prev parent reply other threads:[~2018-06-28 19:04 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-26 17:59 [PATCH v3 0/3] Fix DM DAX handling Ross Zwisler
2018-06-26 17:59 ` [PATCH v3 1/3] pmem: only set QUEUE_FLAG_DAX for fsdax mode Ross Zwisler
2018-06-26 18:52 ` Dan Williams
2018-06-26 18:58 ` Mike Snitzer
2018-06-26 19:07 ` Dan Williams
2018-06-26 19:12 ` Ross Zwisler
2018-06-26 19:13 ` Mike Snitzer
2018-06-26 19:19 ` Dan Williams
2018-06-26 20:54 ` Kani, Toshi
2018-06-26 21:02 ` Dan Williams
2018-06-26 21:23 ` Kani, Toshi
2018-06-26 21:28 ` Dan Williams
2018-06-26 21:31 ` Kani, Toshi
2018-06-26 21:51 ` Dan Williams
2018-06-26 22:04 ` Ross Zwisler
2018-06-28 17:42 ` Kani, Toshi
2018-06-28 17:48 ` Mike Snitzer
2018-06-28 17:59 ` Dan Williams
2018-06-28 18:01 ` Kani, Toshi
2018-06-28 19:04 ` Ross Zwisler [this message]
2018-06-28 19:40 ` Kani, Toshi
2018-06-26 19:11 ` Ross Zwisler
2018-06-26 17:59 ` [PATCH v3 2/3] dax: bdev_dax_supported() check for QUEUE_FLAG_DAX Ross Zwisler
2018-06-26 17:59 ` [PATCH v3 3/3] dm: prevent DAX mounts if not supported Ross Zwisler
2018-06-26 18:17 ` Mike Snitzer
2018-06-26 19:01 ` [PATCH v4 " Ross Zwisler
2018-06-26 18:48 ` [PATCH v3 0/3] Fix DM DAX handling Mike Snitzer
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180628190424.GC17758@linux.intel.com \
--to=ross.zwisler@linux.intel.com \
--cc=dan.j.williams@intel.com \
--cc=dm-devel@redhat.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-nvdimm@lists.01.org \
--cc=linux-xfs@vger.kernel.org \
--cc=snitzer@redhat.com \
--cc=stable@vger.kernel.org \
--cc=toshi.kani@hpe.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).