[PATCH v2] powernv: kvm: make _PAGE_NUMA take effect

Liu ping fan kernelfans at gmail.com
Thu Apr 10 13:28:22 EST 2014

On Mon, Apr 7, 2014 at 4:36 PM, Alexander Graf <agraf at suse.de> wrote:
> On 07.04.14 09:42, Aneesh Kumar K.V wrote:
>> Alexander Graf <agraf at suse.com> writes:
>>> On 03.04.14 04:36, Liu ping fan wrote:
>>>> Hi Alex, could you help to pick up this patch? since  v3.14 kernel can
>>>> enable numa fault for powerpc.
>>> What bad happens without this patch? We map a page even though it was
>>> declared to get NUMA migrated? What happens next?
>> Nothing much, we won't be properly accounting the numa access in the
>> host.  What we want to achieve is to convert a guest access of the page to
>> a host fault so that we can do proper numa access accounting in the
>> host. This would enable us to migrate the page to the correct numa
>> node.
> Ok, so no breakages, just less performance. I wouldn't consider it stable
> material then :).
Sorry to reply late, since I am half out of office during this period.
I am puzzling about you reply.    Without this patch, the guest can
NOT sense the numa changes and ask host to put the pages in right
place.  So the pages which is used by guest will be always misplaced.
The numa-fault method is inspired by real requirement to improve
performance, so we should also consider the performance drop of guest.


> Alex

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