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SubjectRe: [PATCH RFC] hotplug-memory: refactor online_pages to separate zone growth from page onlining
Dave Hansen wrote:
> On Wed, 2008-04-02 at 14:35 -0700, Jeremy Fitzhardinge wrote:
>
>> Dave Hansen wrote:
>>
>>> Oh, once we've let Linux establish ptes to it, we've required that the
>>> hypervisor have it around? How does that work with the balloon driver?
>>> Do we destroy the ptes when giving balloon memory back to the
>>> hypervisor?
>>>
>> Yep. It removes any mapping before handing it back to the hypervisor.
>>
>
> Wow. So does Xen ever use PSE to map kernel data? That sucks.
>

Not at present. But I'd like to change it to manage memory in largepage
chunks so that we can.

> Yeah, but I'm just talking about hotplugged memory. When we add it, we
> don't have to map the added pages (since they're highmem) and don't have
> to touch their contents and zero them out, either. Then, the balloon
> driver can notice that the memory is too large, and start to balloon it
> down.
>

I didn't think x86-64 had a notion of highmem.

How do you prevent the pages from being used before they're ballooned out?

>> Everything also applies to x86-64.
>>
>
> Not really, though. We don't have the page->flags shortage or lack of
> vmemmap on x86_64.

Right now, I'd rather have a single mechanism that works for both.

J


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