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Re: [dm-devel] [RFC PATCH v2] dm mpath: add a queue_if_no_path timeout



On 11/01/13 02:17, Frank Mayhar wrote:
> On Thu, 2013-10-31 at 14:31 +0000, Alasdair G Kergon wrote:
>> (And also remember to test table swap/push back.)
> 
> That brings up something I wanted to ask.  I've dug through the code and
> this particular thing isn't clear to me.  So how does it handle the
> queued I/Os when switching tables?  I see nothing in the table_load()
> path that would deal with this.  I'm guessing that the requests are
> pushed back to the block layer and are later resubmitted and requeued on
> the new multipath queue, but I don't see how that works.
> 
> Code references would be very welcome.

Relevant piece of codes is:
  - multipath_presuspend() temporarily disables "queue_if_no_path"
  - during the suspend process, __must_push_back() catches (otherwise
    failing) requests and requeues them back to the block layer queue
  - upon resume, dm starts processing requests in the block layer queue
    as usual

Hope this helps.
-- 
Jun'ichi Nomura, NEC Corporation


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