Re: [Xen-devel] [PATCH] common/vm_event: Initialize vm_event lists on domain creation

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx> 06/27/17 1:38 PM >>>
>On 06/27/2017 02:26 PM, Jan Beulich wrote:
>>>>> Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx> 06/27/17 10:32 AM >>>
>>> On 06/27/2017 09:21 AM, Jan Beulich wrote:
>>>>>>> Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 06/26/17 5:11 PM >>>
>>>>> There is also a difference in timing; vm_event_init_domain() is called
>>>>> when vm_event is started on the domain, not when the domain is
>>>>> constructed.  IMO, the two should happen at the same time to be
>>>>> consistent.  I'm not fussed at which point, as it would be fine (in
>>>>> principle) for d->vm_event to be NULL in most cases.
>>>>
>>>> I very much support that last aspect - there's shouldn't be any memory
>>>> allocated here if the domain isn't going to make use of VM events.
>>>
>>> Unfortunately it's not as simple as that.
>>>
>>> While I didn't write that code, it would seem that on domain creation
>>> that data is being allocated because it holds information about 3
>>> different vm_event subsystems - monitor, paging, and memshare.
>> 
>> But it can't be that difficult to make it work the suggested way?
>
>We can lazy-allocate that the first time any one of the three gets
>initialized (monitor, paging, share), and update all the code that
>checks d->vm_event->member to check that d->vm_event is not NULL before
>that.
>
>Any objections?

None here.

Jan


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