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SubjectRe: [PATCH v1] powerpc/pseries: CMM: Drop page array
On 25.09.19 09:37, David Hildenbrand wrote:
> On 10.09.19 18:39, David Hildenbrand wrote:
>> We can simply store the pages in a list (page->lru), no need for a
>> separate data structure (+ complicated handling). This is how most
>> other balloon drivers store allocated pages without additional tracking
>> data.
>> For the notifiers, use page_to_pfn() to check if a page is in the
>> applicable range. plpar_page_set_loaned()/plpar_page_set_active() were
>> called with __pa(page_address()) for now, I assume we can simply switch
>> to page_to_phys() here. The pfn_to_kaddr() handling is now mostly gone.
>> Cc: Benjamin Herrenschmidt <>
>> Cc: Paul Mackerras <>
>> Cc: Michael Ellerman <>
>> Cc: Arun KS <>
>> Cc: Pavel Tatashin <>
>> Cc: Thomas Gleixner <>
>> Cc: Andrew Morton <>
>> Cc: Vlastimil Babka <>
>> Signed-off-by: David Hildenbrand <>
>> ---
>> Only compile-tested. I hope the page_to_phys() thingy is correct and I
>> didn't mess up something else / ignoring something important why the array
>> is needed.
>> I stumbled over this while looking at how the memory isolation notifier is
>> used - and wondered why the additional array is necessary. Also, I think
>> by switching to the generic balloon compaction mechanism, we could get
>> rid of the memory hotplug notifier and the memory isolation notifier in
>> this code, as the migration capability of the inflated pages is the real
>> requirement:
>> commit 14b8a76b9d53346f2871bf419da2aaf219940c50
>> Author: Robert Jennings <>
>> Date: Thu Dec 17 14:44:52 2009 +0000
>> powerpc: Make the CMM memory hotplug aware
>> The Collaborative Memory Manager (CMM) module allocates individual pages
>> over time that are not migratable. On a long running system this can
>> severely impact the ability to find enough pages to support a hotplug
>> memory remove operation.
>> [...]
>> Thoughts?
> Ping, is still feature still used at all?
> If nobody can test, any advise on which HW I need and how to trigger it?

So ... if CMM is no longer alive I propose ripping it out completely.
Does anybody know if this feature is still getting used? Getting rid of
the memory isolation notifier sounds desirable - either by scrapping CMM
or by properly wiring up balloon compaction.



David / dhildenb

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