From: Dario Faggioli <raistlin@linux.it>
To: George Shuklin <george.shuklin@gmail.com>
Cc: xen-devel@lists.xen.org
Subject: Re: domain creation vs querying free memory (xend and xl)
Date: Fri, 28 Sep 2012 18:08:03 +0200 [thread overview]
Message-ID: <1348848483.3153.23.camel@Abyss> (raw)
In-Reply-To: <50646FBF.9000501@gmail.com>
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On Thu, 2012-09-27 at 19:24 +0400, George Shuklin wrote:
> not sure about xl/xm, but xapi performs one start at time, so there is
> no race between domains for memory or other resources.
>
IIRC, xl has a vary coarse grain locking mechanism in place for domain
creation too. As a result of that, you shouldn't be able to create two
domains at the same time, which should be enough for preventing the
situation described in the original e-mail for occurring.
Looking at acquire_lock() and release_lock() (and at where they are
called) in xl code should clarify whether or not that is enough to
actually avoid the race (which I think it is, but I might be wrong :-D).
That being said, there still is the room for races, although not wrt
domain creation, as, for instance, there isn't any synchronization
between creation and ballooning, which both manipulate memory. So, maybe
thinking about some kind of reservation-based/transactional mechanism at
some level might make actual sense.
Unfortunately, I've no idea about how xm works in that respect.
Hope this at least help clarifying the situation a bit. :-)
Thanks and Regards,
Dario
--
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://retis.sssup.it/people/faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
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next prev parent reply other threads:[~2012-09-28 16:08 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-26 21:17 domain creation vs querying free memory (xend and xl) Dan Magenheimer
2012-09-27 11:26 ` Konrad Rzeszutek Wilk
2012-09-27 15:32 ` Dan Magenheimer
2012-09-27 15:24 ` George Shuklin
2012-09-28 16:08 ` Dario Faggioli [this message]
2012-10-02 18:17 ` Dan Magenheimer
2012-09-28 17:12 ` Ian Jackson
2012-10-01 20:03 ` Dan Magenheimer
2012-10-02 9:10 ` Tim Deegan
2012-10-02 9:47 ` Ian Campbell
2012-10-02 19:33 ` Dan Magenheimer
2012-10-02 20:16 ` Tim Deegan
2012-10-02 21:56 ` Dan Magenheimer
2012-10-04 10:06 ` Tim Deegan
2012-10-04 10:17 ` Ian Campbell
2012-10-04 13:20 ` Andres Lagar-Cavilla
2012-10-04 13:25 ` Ian Campbell
2012-10-04 16:54 ` Dan Magenheimer
2012-10-04 17:00 ` Andres Lagar-Cavilla
2012-10-05 9:44 ` Ian Campbell
2012-10-05 11:40 ` George Dunlap
2012-10-08 1:02 ` Dan Magenheimer
2012-10-16 11:49 ` George Dunlap
2012-10-16 17:51 ` Dan Magenheimer
2012-10-17 17:35 ` George Dunlap
2012-10-17 18:33 ` Andres Lagar-Cavilla
2012-10-17 19:46 ` Dan Magenheimer
2012-10-17 20:14 ` Andres Lagar-Cavilla
2012-10-17 22:07 ` Dan Magenheimer
2012-10-17 18:45 ` Dan Magenheimer
2012-10-17 17:35 ` George Dunlap
2012-10-04 13:33 ` Andres Lagar-Cavilla
2012-10-04 16:59 ` Dan Magenheimer
2012-10-04 17:08 ` Andres Lagar-Cavilla
2012-10-04 17:18 ` Dan Magenheimer
2012-10-04 17:30 ` Andres Lagar-Cavilla
2012-10-04 17:55 ` Dan Magenheimer
2012-10-05 14:25 ` Andres Lagar-Cavilla
2012-10-07 23:43 ` Dan Magenheimer
2012-10-04 16:36 ` Dan Magenheimer
2012-10-04 18:26 ` Olaf Hering
2012-10-04 19:38 ` Dan Magenheimer
2012-10-04 20:18 ` Olaf Hering
2012-10-04 20:35 ` Dan Magenheimer
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