On Thu 16-06-11 12:57:41, KAMEZAWA Hiroyuki wrote:

From 4fbd49697456c227c86f1d5b46f2cd2169bf1c5b Mon Sep 17 00:00:00 2001
From: KAMEZAWA Hiroyuki <redacted>
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
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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