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SubjectRe: [patch 0/3] mm: improve page aging fairness between zones/nodes
On 24.07.2013 13:18, Zlatko Calusic wrote:
> On 22.07.2013 18:48, Zlatko Calusic wrote:
>> On 19.07.2013 22:55, Johannes Weiner wrote:
>>> The way the page allocator interacts with kswapd creates aging
>>> imbalances, where the amount of time a userspace page gets in memory
>>> under reclaim pressure is dependent on which zone, which node the
>>> allocator took the page frame from.
>>>
>>> #1 fixes missed kswapd wakeups on NUMA systems, which lead to some
>>> nodes falling behind for a full reclaim cycle relative to the other
>>> nodes in the system
>>>
>>> #3 fixes an interaction where kswapd and a continuous stream of page
>>> allocations keep the preferred zone of a task between the high and
>>> low watermark (allocations succeed + kswapd does not go to sleep)
>>> indefinitely, completely underutilizing the lower zones and
>>> thrashing on the preferred zone
>>>
>>> These patches are the aging fairness part of the thrash-detection
>>> based file LRU balancing. Andrea recommended to submit them
>>> separately as they are bugfixes in their own right.
>>>
>>
>> I have the patch applied and under testing. So far, so good. It looks
>> like it could finally fix the bug that I was chasing few months ago
>> (nicely described in your bullet #3). But, few more days of testing will
>> be needed before I can reach a quality verdict.
>>
>
> Well, only 2 days later it's already obvious that the patch is perfect! :)
>

Additionaly, on the patched kernel, kswapd burns 30% less CPU cycles.
Nice to see that restored balance also eases kswapd's job, but that was
to be expected. Measured on the real workload, twice, to be sure.

Regards,
--
Zlatko



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