Messages in this thread | | | From | "Kani, Toshi" <> | Subject | Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG_DAX for fsdax mode | Date | Tue, 26 Jun 2018 20:54:03 +0000 |
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On Tue, 2018-06-26 at 15:13 -0400, Mike Snitzer wrote: > On Tue, Jun 26 2018 at 3:07pm -0400, > Dan Williams <dan.j.williams@intel.com> wrote: > > > On Tue, Jun 26, 2018 at 11:58 AM, Mike Snitzer <snitzer@redhat.com> wrote: > > > On Tue, Jun 26 2018 at 2:52pm -0400, > > > Dan Williams <dan.j.williams@intel.com> wrote: > > > > > > > On Tue, Jun 26, 2018 at 10:59 AM, Ross Zwisler > > > > <ross.zwisler@linux.intel.com> wrote: > > > > > QUEUE_FLAG_DAX is an indication that a given block device supports > > > > > filesystem DAX and should not be set for PMEM namespaces which are in "raw" > > > > > or "sector" modes. These namespaces lack struct page and are prevented > > > > > from participating in filesystem DAX. > > > > > > > > > > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> > > > > > Suggested-by: Mike Snitzer <snitzer@redhat.com> > > > > > Cc: stable@vger.kernel.org > > > > > > > > Why is this cc: stable? What is the user visible impact of this change > > > > especially given the requirement to validate QUEUE_FLAG_DAX with > > > > bdev_dax_supported()? Patch looks good, but it's just a cosmetic fixup > > > > afaics. > > > > > > This isn't cosmetic when you consider that stacking up a DM device is > > > looking at this flag to determine whether a table does or does _not_ > > > support DAX. > > > > > > So this patch, in conjunction with the other changes in the series, is > > > certainly something I'd consider appropriate for stable. > > > > I think this classifies as something that never worked correctly and > > is not a regression. It does not identify which commit it is repairing > > or the user visible failure mode. > > So you're taking issue with making stacked dax configs work in older > kernels? That's fine. We can drop the stable cc if you like. > > But I mean we intended for this to work.. so the Fixes commit references > can easily be added, e.g.: 545ed20e6df68a4d2584a29a2a28ee8b2f7e9547 > ("dm: add infrastructure for DAX support")
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.
Thanks, -Toshi
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