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Date:   Wed, 6 Jun 2018 12:16:19 -0600
From:   Ross Zwisler <ross.zwisler@linux.intel.com>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Ross Zwisler <ross.zwisler@linux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dave Jiang <dave.jiang@intel.com>,
        linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: [PATCH v3 2/4] libnvdimm: unconditionally deep flush on *sync
Message-ID: <20180606181619.GA13076@linux.intel.com>
References: <20180606164515.25677-1-ross.zwisler@linux.intel.com>
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On Wed, Jun 06, 2018 at 10:57:59AM -0700, Dan Williams wrote:
> On Wed, Jun 6, 2018 at 9:45 AM, Ross Zwisler
> <ross.zwisler@linux.intel.com> wrote:
> > Prior to this commit we would only do a "deep flush" (have nvdimm_flush()
> > write to each of the flush hints for a region) in response to an
> > msync/fsync/sync call if the nvdimm_has_cache() returned true at the time
> > we were setting up the request queue.  This happens due to the write cache
> > value passed in to blk_queue_write_cache(), which then causes the block
> > layer to send down BIOs with REQ_FUA and REQ_PREFLUSH set.  We do have a
> > "write_cache" sysfs entry for namespaces, i.e.:
> >
> >   /sys/bus/nd/devices/pfn0.1/block/pmem0/dax/write_cache
> >
> > which can be used to control whether or not the kernel thinks a given
> > namespace has a write cache, but this didn't modify the deep flush behavior
> > that we set up when the driver was initialized.  Instead, it only modified
> > whether or not DAX would flush CPU caches via dax_flush() in response to
> > *sync calls.
> >
> > Simplify this by making the *sync deep flush always happen, regardless of
> > the write cache setting of a namespace.  The DAX CPU cache flushing will
> > still be controlled the write_cache setting of the namespace.
> >
> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> > Suggested-by: Dan Williams <dan.j.williams@intel.com>
> 
> Looks, good. I believe we want this one and ["PATCH v3 4/4] libnvdimm:
> don't flush power-fail protected CPU caches" marked for -stable and
> tagged with:
> 
> Fixes: 5fdf8e5ba566 ("libnvdimm: re-enable deep flush for pmem devices
> via fsync()")
> 
> ...any concerns with that?

Nope, sounds good.  Can you fix that up when you apply, or would it be helpful
for me to send another revision with those tags?