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Re: [Xen-devel] [PATCH v3 4/9] mm: Scrub memory from idle loop

On 05/05/2017 10:51 AM, Jan Beulich wrote:
>>>> On 05.05.17 at 16:27, <boris.ostrovsky@xxxxxxxxxx> wrote:
>> On 05/05/2017 10:14 AM, Jan Beulich wrote:
>>>>>> On 05.05.17 at 16:10, <JBeulich@xxxxxxxx> wrote:
>>>>>>> On 05.05.17 at 15:42, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>>>>>>> Otoh there's not much to scrub yet until Dom0 had all its memory
>>>>>>>> allocated, and we know which pages truly remain free (wanting
>>>>>>>> what is currently the boot time scrubbing done on them). But that
>>>>>>>> point in time may still be earlier than when we switch to
>>>>>>>> SYS_STATE_active.
>>>>>> IOW I think boot scrubbing could be kicked off as soon as Dom0
>>>>>> had the bulk of its memory allocated.
>>>>> Since we only are trying to avoid mapcache vcpu override can't we just
>>>>> scrub whenever override is NULL (per-cpu or not)?
>>>> But how do you know? The variable should remain static in
>>>> domain_page.c, so I think we'd instead need a notification to
>>>> the scrubber when it gets set back to NULL.
>> Why not just have in domain_page.c
>> bool mapcache_override() {return override != NULL;}
>> (or appropriate per-cpu variant)?
> And you would mean to permanently poll this?

We have to permanently poll on/check something. Either it will be local
to page_alloc.c or to domain_page.c.


>>> And of course if the override variable was per-CPU, you wouldn't
>>> have a need to know, as you wouldn't try scrubbing on the CPU
>>> doing the Dom0 setup.
>> Actually, won't (override != current) do the trick?
> This is like saying "If I don't get a car, it should be a red one." If
> you don't need to know, how can it matter what expression to use?
> Jan

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