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

From: Michal Hocko
Date: Thu Jun 23 2011 - 09:48:56 EST

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@xxxxxxxxxxxxxx>
> 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?

Michal Hocko
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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