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SubjectRe: [PATCH RFC] hotplug-memory: refactor online_pages to separate zone growth from page onlining
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.

> If we're talking about i386, then we're set. We don't map the hot-added
> memory at all because we only add highmem on i386. The only time we map
> these pages is *after* we actually allocate them when they get mapped
> into userspace or used as vmalloc() or they're kmap()'d.
>

Well, the balloon driver can balloon out lowmem pages, so we have to
deal with mappings either way. But balloon+hotplug would work
identically on x86-64, so all pages are mapped.

>> I think we're getting off track here; this is a lot of extra complexity
>> to justify allowing usermode to use /sys to online a chunk of hotplugged
>> memory.
>>
>
> Either that, or we're going to develop the entire Xen/kvm memory hotplug
> architecture around the soon-to-be-legacy i386 limitations. :)

Everything also applies to x86-64.


J


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