Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush()

From	Dan Williams <dan.j.williams@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush()
Date	2017-04-24 18:40 +0200
Message-ID	<tzPbR-Ue-23@gated-at.bofh.it> (permalink)
References	<tyQD0-3JK-7@gated-at.bofh.it> <tzP2a-Rd-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, Apr 24, 2017 at 9:26 AM, Jeff Moyer <jmoyer@redhat.com> wrote:
> Dan Williams <dan.j.williams@intel.com> writes:
>
>> The nvdimm_flush() mechanism helps to reduce the impact of an ADR
>> (asynchronous-dimm-refresh) failure. The ADR mechanism handles flushing
>> platform WPQ (write-pending-queue) buffers when power is removed. The
>> nvdimm_flush() mechanism performs that same function on-demand.
>>
>> When a pmem namespace is associated with a block device, an
>> nvdimm_flush() is triggered with every block-layer REQ_FUA, or REQ_FLUSH
>> request. However, when a namespace is in device-dax mode, or namespaces
>> are disabled, userspace needs another path.
>>
>> The new 'flush' attribute is visible when it can be determined that the
>> interleave-set either does, or does not have DIMMs that expose WPQ-flush
>> addresses, "flush-hints" in ACPI NFIT terminology. It returns "1" and
>> flushes DIMMs, or returns "0" the flush operation is a platform nop.
>>
>> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
>
> NACK.  This should function the same way it does for a pmem device.
> Wire up sync.

We don't have dirty page tracking for device-dax, without that I don't
think we should wire up the current sync calls. I do think we need a
more sophisticated sync syscall interface eventually that can select
which level of flushing is being performed (page cache vs cpu cache vs
platform-write-buffers). Until then I think this sideband interface
makes sense and sysfs is more usable than an ioctl.

Thread

[PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush() Dan Williams <dan.j.williams@intel.com> - 2017-04-22 02:00 +0200
  Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush() Masayoshi Mizuma <m.mizuma@jp.fujitsu.com> - 2017-04-24 07:50 +0200
    Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush() Dan Williams <dan.j.williams@intel.com> - 2017-04-24 09:10 +0200
  Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush() Jeff Moyer <jmoyer@redhat.com> - 2017-04-24 18:30 +0200
    Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush() Dan Williams <dan.j.williams@intel.com> - 2017-04-24 18:40 +0200
      Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush() Jeff Moyer <jmoyer@redhat.com> - 2017-04-24 18:50 +0200
        Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush() Dan Williams <dan.j.williams@intel.com> - 2017-04-24 19:50 +0200
          Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush() Jeff Moyer <jmoyer@redhat.com> - 2017-04-24 20:00 +0200
  Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush() Dan Williams <dan.j.williams@intel.com> - 2017-04-24 19:10 +0200

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