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Re: [Xen-devel] [PATCH 2/9] vm_event: Define VM_EVENT type
- To: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 4 Jun 2019 17:09:11 +0100
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- Cc: Petre Pircalabu <ppircalabu@xxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 04 Jun 2019 16:09:19 +0000
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On 03/06/2019 23:26, Tamas K Lengyel wrote:
> On Mon, Jun 3, 2019 at 4:22 PM Tamas K Lengyel <tamas@xxxxxxxxxxxxx> wrote:
>>>> /* XEN_DOMCTL_mem_sharing_op.
>>>> - * The CONTROL sub-domctl is used for bringup/teardown. */
>>>> + * The CONTROL sub-domctl is used for bringup/teardown.
>>>> + * Please note that mem sharing can be turned on *without* setting-up the
>>>> + * correspondin ring
>>>> + */
>>> As a tangent, it can? how? (I'm entirely prepared to believe that this
>>> is how the code currently works, but I can't see how such a setup would
>>> plausibly work.)
>> The vm_event ring for mem_sharing is only used to communicate
>> out-of-memory condition to an external listener. I think it's only
>> useful for logging since the listener wouldn't really be in a position
>> to try to "make space" for the faulting domain and it would get
>> destroyed after the message is sent. In any case, there isn't any
>> documentation for how it was intended to be used so this is just my
>> guess.
> Actually, it seems the listener was intended to be able to try to
> "make space" for the domain. How exactly is not clear but anyway, the
> domain would get paused if there is a listener instead of just being
> destroyed when there is an ENOMEM error while trying to deduplicate
> shared pages.
I can't say I'm surprised by this...
~Andrew
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