linux-kernel - Re: [PATCH v2 3/3] libnvdimm: don't flush power-fail protected CPU caches

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Date:   Wed, 6 Jun 2018 09:30:59 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Jiang <dave.jiang@...el.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>
Subject: Re: [PATCH v2 3/3] libnvdimm: don't flush power-fail protected CPU
 caches

On Tue, Jun 05, 2018 at 07:00:14PM -0700, Dan Williams wrote:
> On Tue, Jun 5, 2018 at 4:58 PM, Ross Zwisler
> <ross.zwisler@...ux.intel.com> wrote:
> > This commit:
> >
> > 5fdf8e5ba566 ("libnvdimm: re-enable deep flush for pmem devices via fsync()")
> >
> > intended to make sure that deep flush was always available even on
> > platforms which support a power-fail protected CPU cache.  An unintended
> > side effect of this change was that we also lost the ability to skip
> > flushing CPU caches on those power-fail protected CPU cache.
> >
> > Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > Fixes: 5fdf8e5ba566 ("libnvdimm: re-enable deep flush for pmem devices via fsync()")
> > ---
> >  drivers/dax/super.c   | 14 +++++++++++++-
> >  drivers/nvdimm/pmem.c |  2 ++
> >  include/linux/dax.h   |  4 ++++
> >  3 files changed, 19 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index c2c46f96b18c..80253c531a9b 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -152,6 +152,8 @@ enum dax_device_flags {
> >         DAXDEV_ALIVE,
> >         /* gate whether dax_flush() calls the low level flush routine */
> >         DAXDEV_WRITE_CACHE,
> > +       /* only flush the CPU caches if they are not power fail protected */
> > +       DAXDEV_FLUSH_ON_SYNC,
> 
> I'm not grokking why we need DAXDEV_FLUSH_ON_SYNC. The power fail
> protected status of the cache only determines the default for
> DAXDEV_WRITE_CACHE.

Ah, yea, that's much cleaner.  I'll send out a v3.