linux-kernel - Re: [PATCH V3] memcg, oom: provide more precise dump info while memcg oom happening

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Date:	Fri, 9 Nov 2012 11:50:52 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Sha Zhengju <handai.szj@...il.com>
Cc:	linux-mm@...ck.org, cgroups@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com, akpm@...ux-foundation.org,
	rientjes@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] memcg, oom: provide more precise dump info while
 memcg oom happening

On Fri 09-11-12 18:23:07, Sha Zhengju wrote:
> On 11/09/2012 12:25 AM, Michal Hocko wrote:
> >On Thu 08-11-12 23:52:47, Sha Zhengju wrote:
[...]
> >>+	for (i = 0; i<  MEM_CGROUP_STAT_NSTATS; i++) {
> >>+		long long val = 0;
> >>+		if (i == MEM_CGROUP_STAT_SWAP&&  !do_swap_account)
> >>+			continue;
> >>+		for_each_mem_cgroup_tree(mi, memcg)
> >>+			val += mem_cgroup_read_stat(mi, i);
> >>+		printk(KERN_CONT "%s:%lldKB ", mem_cgroup_stat_names[i], K(val));
> >>+	}
> >>+
> >>+	for (i = 0; i<  NR_LRU_LISTS; i++) {
> >>+		unsigned long long val = 0;
> >>+
> >>+		for_each_mem_cgroup_tree(mi, memcg)
> >>+			val += mem_cgroup_nr_lru_pages(mi, BIT(i));
> >>+		printk(KERN_CONT "%s:%lluKB ", mem_cgroup_lru_names[i], K(val));
> >>+	}
> >>+	printk(KERN_CONT "\n");
> >This is nice and simple I am just thinking whether it is enough. Say
> >that you have a deeper hierarchy and the there is a safety limit in the
> >its root
> >         A (limit)
> >        /|\
> >       B C D
> >           |\
> >	  E F
> >
> >and we trigger an OOM on the A's limit. Now we know that something blew
> >up but what it was we do not know. Wouldn't it be better to swap the for
> >and for_each_mem_cgroup_tree loops? Then we would see the whole
> >hierarchy and can potentially point at the group which doesn't behave.
> >Memory cgroup stats for A/: ...
> >Memory cgroup stats for A/B/: ...
> >Memory cgroup stats for A/C/: ...
> >Memory cgroup stats for A/D/: ...
> >Memory cgroup stats for A/D/E/: ...
> >Memory cgroup stats for A/D/F/: ...
> >
> >Would it still fit in with your use case?
> >[...]
> 
> We haven't used those complicate hierarchy yet, but it sounds a good
> suggestion. :)
> Hierarchy is a little complex to use from our experience, and the
> three cgroups involved in memcg oom can be different: memcg of
> invoker, killed task, memcg of going over limit.Suppose a process in
> B triggers oom and a victim in root A is selected to be killed, we
> may as well want to know memcg stats just local in A cgroup(excludes
> BCD). So besides hierarchy info, does it acceptable to also print
> the local root node stats which as I did in the V1
> version(https://lkml.org/lkml/2012/7/30/179).

Ohh, I probably wasn't clear enough. I didn't suggest cumulative
numbers. Only per group. So it would be something like:

	for_each_mem_cgroup_tree(mi, memcg) {
		printk("Memory cgroup stats for %s", memcg_name);
		for (i = 0; i<  MEM_CGROUP_STAT_NSTATS; i++) {
			if (i == MEM_CGROUP_STAT_SWAP&&  !do_swap_account)
				continue;
			printk(KERN_CONT "%s:%lldKB ", mem_cgroup_stat_names[i],
				K(mem_cgroup_read_stat(mi, i)));
		}
		for (i = 0; i<  NR_LRU_LISTS; i++)
			printk(KERN_CONT "%s:%lluKB ", mem_cgroup_lru_names[i],
				K(mem_cgroup_nr_lru_pages(mi, BIT(i))));

		printk(KERN_CONT"\n");
	}

> Another one I'm hesitating is numa stats, it seems the output is
> beginning to get more and more....

NUMA stats are basically per node - per zone LRU data and that the
for(NR_LRU_LISTS) can be easily extended to cover that.
-- 
Michal Hocko
SUSE Labs
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