linux-kernel - Re: [PATCH v2] libnvdimm: re-enable deep flush for pmem devices

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Date:   Mon, 12 Feb 2018 16:08:54 -0700
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Jeff Moyer <jmoyer@...hat.com>,
        "Zwisler, Ross" <ross.zwisler@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm@...ts.01.org
Subject: Re: [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@...hat.com> wrote:
> > Dave Jiang <dave.jiang@...el.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@...el.com>
>     Signed-off-by: Dan Williams <dan.j.williams@...el.com>

Plus Jeff's reviewed-by.