Re: [patch -mm 1/2] oom: badness heuristic rewrite

[David Rientjes <rientjes@google.com>]

On Tue, 3 Aug 2010, KAMEZAWA Hiroyuki wrote:

> > Sure, a task could be killed with a very low /proc/pid/oom_score, but only 
> > if its cpuset is oom, for example, and it has the highest score of all 
> > tasks attached to that oom_score.  So /proc/pid/oom_score needs to be 
> > considered in the context in which the oom occurs: system-wide, cpuset, 
> > mempolicy, or memcg.  That's unchanged from the old oom killer.
> > 
> 
> unchanged ?
> 

Oh, I meant the fact that a task with a low oom_score compared to other 
system tasks may be killed because a cpuset is oom, for instance, is 
unchanged because we only kill tasks that are constrained to that cpuset.

> Assume 2 proceses A, B which has oom_score_adj of 300 and 0
> And A uses 200M, B uses 1G of memory under 4G system
> 
> Under the system. 
> 	A's socre = (200M *1000)/4G + 300 = 350
> 	B's score = (1G * 1000)/4G = 250.

Right, A is penalized 30% of system memory and its use is ~5%, resulting 
in a score of 350, or 35%.  B's use is 25%.

> In the cpuset, it has 2G of memory.
> 	A's score = (200M * 1000)/2G + 300 = 400
> 	B's socre = (1G * 1000)/2G = 500
> 
> This priority-inversion don't happen in current system.
> 

Yes, but this is what oom_score_adj is intended to do: an oom_score_adj of 
300 means task A should be penalized 30% of available memory.  A positive 
oom_score_adj typically means "all other competing tasks should be allowed 
30% more memory, cumulatively, compared to this task."  Task A uses ~10% 
of available memory and task B uses 50% of available memory.  That's a 40% 
difference, which is greater than task A's penalization of 30%, so B is 
killed.

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