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

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

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?


Thanks,
Razvan

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