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SubjectRe: [PATCH v2] libnvdimm: re-enable deep flush for pmem devices
On Mon, Feb 12, 2018 at 03:05:10PM -0800, Dan Williams wrote:
> On Mon, Feb 12, 2018 at 2:53 PM, Jeff Moyer <jmoyer@redhat.com> wrote:
> > Dave Jiang <dave.jiang@intel.com> writes:
> >
> >> Re-enable deep flush so that users always have a way to be sure that a write
> >> does make it all the way out to the NVDIMM. The PMEM driver writes always
> >> make it "all the way to the NVDIMM", and it relies on the ADR mechanism to
> >> flush the write buffers on power failure. Deep flush is there to explicitly
> >> flush those write buffers to protect against (rare) ADR failure.
> >> This change prevents a regression in deep flush behavior so that applications
> >> can continue to depend on fsync() as a mechanism to trigger deep flush in the
> >> filesystem-dax case.
> >
> > That's still very confusing text. Specifically, the part where you say
> > that pmem driver writes always make it to the DIMM. I think the
> > changelog could start with "Deep flush is there to explicitly flush
> > write buffers...." Anyway, the fix looks right to me.
>
> I ended up changing the commit message to this, let me know if it reads better:
>
>
> libnvdimm: re-enable deep flush for pmem devices via fsync()
>
> Re-enable deep flush so that users always have a way to be sure that a
> write makes it all the way out to media. The PMEM driver writes always
> arrive at the NVDIMM, and it relies on the ADR (Asynchronous DRAM
> Refresh) mechanism to flush the write buffers on power failure. Deep
> flush is there to explicitly flush those write buffers to protect
> against (rare) ADR failure. This change prevents a regression in deep
> flush behavior so that applications can continue to depend on fsync() as
> a mechanism to trigger deep flush in the filesystem-DAX case.
>
> Fixes: 06e8ccdab15f4 ("acpi: nfit: Add support for detect platform
> CPU cache...")
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Plus Jeff's reviewed-by.

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