Messages in this thread | | | Date | Wed, 02 Apr 2008 16:36:36 -0500 | From | Anthony Liguori <> | Subject | Re: [PATCH RFC] hotplug-memory: refactor online_pages to separate zone growth from page onlining |
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Dave Hansen wrote: > On Wed, 2008-04-02 at 14:03 -0700, Jeremy Fitzhardinge wrote: > >> Dave Hansen wrote: >> No, not in a Xen direct-pagetable guest. The guest actually sees real >> hardware page numbers (mfns) when the hypervisor gives it a page. By >> the time the hypervisor gives it a page reference, it already >> guaranteeing that the page is available for guest use. The only thing >> that we could do is prevent the guest from mapping the page, but that >> doesn't really achieve much. >> > > 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? > > 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. > > >> 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. :) >
s:Xen/kvm:Xen:g
We don't need anything special for KVM. Bare metal memory hotplug should be sufficient provided userspace udev scripts are properly configured to offline memory automatically.
Regards,
Anthony Liguori
> -- Dave > >
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