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SubjectRe: [PATCH 28/40] autonuma: make khugepaged pte_numa aware
On 07/12/2012 02:50 PM, Andrea Arcangeli wrote:
> On Mon, Jul 02, 2012 at 12:24:36AM -0400, Rik van Riel wrote:
>> On 06/28/2012 08:56 AM, Andrea Arcangeli wrote:
>>> If any of the ptes that khugepaged is collapsing was a pte_numa, the
>>> resulting trans huge pmd will be a pmd_numa too.
>>
>> Why?
>>
>> If some of the ptes already got faulted in and made really
>> resident again, why do you want to incur a new NUMA fault
>> on the newly collapsed hugepage?
>
> If we don't set pmd_numa on the collapsed hugepage, the result is that
> we'll understimate the thread NUMA affinity to the node where the
> hugepage is located (mm affinity is recorded independently by the NUMA
> hinting page faults).
>
> If it's better or worse I guess depends on luck, we just lose
> information.

Fair enough.






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