Re: [PATCH 7/7] memcg: proportional fair vicitm node selection

[Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>]

2011/6/23 Michal Hocko <mhocko@suse.cz>:
> On Thu 16-06-11 12:57:41, KAMEZAWA Hiroyuki wrote:
>> From 4fbd49697456c227c86f1d5b46f2cd2169bf1c5b Mon Sep 17 00:00:00 2001
>> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> Date: Thu, 16 Jun 2011 11:25:23 +0900
>> Subject: [PATCH 7/7] memcg: proportional fair node vicitm selection
>>
>> commit 889976 implements a round-robin scan of numa nodes for
>> LRU scanning of memcg at hitting limit.
>> But, round-robin is not very good.
>>
>> This patch implements a proportionally fair victim selection of nodes
>> rather than round-robin. The logic is fair against each node's weight.
>>
>> Each node's weight is calculated periodically and we build an node's
>> scheduling entity as
>>
>>      total_ticket = 0;
>>      for_each_node(node)
>>       node->ticket_start =  total_ticket;
>>         node->ticket_end   =  total_ticket + this_node's_weight()
>>         total_ticket = node->ticket_end;
>>
>> Then, each nodes has some amounts of tickets in proportion to its own weight.
>>
>> At selecting victim, a random number is selected and the node which contains
>> the random number in [ticket_start, ticket_end) is selected as vicitm.
>> This is a lottery scheduling algorithm.
>>
>> For quick search of victim, this patch uses bsearch().
>>
>> Test result:
>>   on 8cpu box with 2 nodes.
>>   limit memory to be 300MB and run httpd for 4096files/600MB working set.
>>   do (normalized) random access by apache-bench and see scan_stat.
>>   The test makes 40960 request. and see scan_stat.
>>   (Because a httpd thread just use 10% cpu, the number of threads will
>>    not be balanced between nodes. Then, file caches will not be balanced
>>    between nodes.)
>
> Have you also tried to test with balanced nodes? I mean, is there any
> measurable overhead?
>

Not enough yet. I checked OOM trouble this week :).

I may need to make another fake_numa setup + cpuset
to measurements. In usual path, new overhead is random32() and
bsearch().  I'll do some.

Thanks,
-Kame

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