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Re: [PATCH 1/2] block: generic request_queue reference counting

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On Sun, Oct 4, 2015 at 12:52 AM, Ming Lei <tom.leiming@gmail.com> wrote:
> On Wed, Sep 30, 2015 at 8:41 AM, Dan Williams <dan.j.williams@intel.com> wrote:
>> Allow pmem, and other synchronous/bio-based block drivers, to fallback
>
> Just a bit curious, why not extend it for all(both synchronous and
> asynchrounous) bio-based drivers? As you mentioned in introductory
> message, all bio based drivers may have this kind of problem.
>
> One idea I thought of is to hold the usage counter in bio life time,
> instead of request's life time like in blk-mq.
>
>> on a per-cpu reference count managed by the core for tracking queue
>> live/dead state.
>>
>> The existing per-cpu reference count for the blk_mq case is promoted to
>> be used in all block i/o scenarios.  This involves initializing it by
>> default, waiting for it to drop to zero at exit, and holding a live
>> reference over the invocation of q->make_request_fn() in
>
> It isn't enough for asynchrounous bio drivers.

True, but I think that support is a follow on extension of the
mechanism.  It seems to me not as straightforward as holding a
per-request reference or a reference over the submission path.
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[PATCH 0/2] block drivers + dax vs driver unbind Dan Williams <dan.j.williams@intel.com> - 2015-09-30 02:50 +0200
  [PATCH 2/2] block, dax: fix lifetime of in-kernel dax mappings Dan Williams <dan.j.williams@intel.com> - 2015-09-30 02:50 +0200
    Re: [PATCH 2/2] block, dax: fix lifetime of in-kernel dax mappings Dave Chinner <david@fromorbit.com> - 2015-10-01 01:40 +0200
      Re: [PATCH 2/2] block, dax: fix lifetime of in-kernel dax mappings Dan Williams <dan.j.williams@intel.com> - 2015-10-01 02:20 +0200
      Re: [PATCH 2/2] block, dax: fix lifetime of in-kernel dax mappings Dan Williams <dan.j.williams@intel.com> - 2015-10-06 04:00 +0200
        Re: [PATCH 2/2] block, dax: fix lifetime of in-kernel dax mappings Dave Chinner <david@fromorbit.com> - 2015-10-06 23:20 +0200
  [PATCH 1/2] block: generic request_queue reference counting Dan Williams <dan.j.williams@intel.com> - 2015-09-30 02:50 +0200
    Re: [PATCH 1/2] block: generic request_queue reference counting Christoph Hellwig <hch@lst.de> - 2015-10-04 08:50 +0200
      Re: [PATCH 1/2] block: generic request_queue reference counting Dan Williams <dan.j.williams@intel.com> - 2015-10-06 01:50 +0200
    Re: [PATCH 1/2] block: generic request_queue reference counting Ming Lei <tom.leiming@gmail.com> - 2015-10-04 10:00 +0200
      Re: [PATCH 1/2] block: generic request_queue reference counting Dan Williams <dan.j.williams@intel.com> - 2015-10-06 01:30 +0200
        Re: [PATCH 1/2] block: generic request_queue reference counting Ming Lei <tom.leiming@gmail.com> - 2015-10-06 12:50 +0200
          Re: [PATCH 1/2] block: generic request_queue reference counting Dan Williams <dan.j.williams@intel.com> - 2015-10-06 18:10 +0200

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