Re: [patch 0/3] mm: improve page aging fairness between zones/nodes

[Zlatko Calusic <zcalusic@bitsync.net>]

On 24.07.2013 14:46, Hush Bensen wrote:
> ao? 2013/7/24 19:18, Zlatko Calusic a??e??:
>> 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! :)
>>
>> In the attached image, in the left column are the graphs covering last
>> day and a half. It can be observed that zones are really balanced, and
>> that aging is practically perfect. Graphs on the right column cover
>> last 10 day period, and the left side of the upper graph shows how it
>> would look with the stock kernel after about 20 day uptime (although
>> only a few days is enough to reach such imbalance). File pages in the
>> Normal zone are extinct species (red) and the zone is choke full of
>> anon pages (blue). Having seen a lot of this graphs, I'm certain that
>> it won't happen anymore with your patch applied. The balance is
>> restored! Thank you for your work. Feel free to add:
>>
>> Tested-by: Zlatko Calusic <zcalusic@bitsync.net>
>
> Thanks for your testing Zlatko, could you tell me which benchmark or
> workload you are using? Btw, which tool is used to draw these nice
> pictures? ;-)
>

Workload is mixed (various services, light load). What makes the biggest 
I/O load is backup procedure that goes every evening. The graphs are 
home-made, a little bit of rrd, a little bit of perl, nothing too 
complex. I'm actually slowly getting rid of these extra graphs, because 
I used them only for debugging this specific problem, which is now fixed 
thanks to Johannes.

-- 
Zlatko

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