Re: [patch] memcg: add oom killer delay

On Mon, 7 Feb 2011 18:13:22 -0800 (PST)
David Rientjes [off-list ref] wrote:

On Tue, 8 Feb 2011, KAMEZAWA Hiroyuki wrote:

quoted

quoted

+static int mem_cgroup_oom_delay_millisecs_write(struct cgroup *cgrp,
+					struct cftype *cft, u64 val)
+{
+	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
+	struct mem_cgroup *iter;
+
+	if (val > MAX_SCHEDULE_TIMEOUT)
+		return -EINVAL;
+
+	for_each_mem_cgroup_tree(iter, memcg) {
+		iter->oom_delay = msecs_to_jiffies(val);
+		memcg_oom_recover(iter);
+	}
+	return 0;

Seems nicer and it seems you tries to update all children cgroups.

BTW, with above code, with following heirarchy,

    A
   /
  B  
 /
C

When a user set oom_delay in order as A->B->C, A,B,C can have 'different' numbers.
When a user set oom_delay in order as C->B->A, A,B,C will have the same numbers.

This intreface seems magical, or broken.

It's not really magical, it just means that if you change the delay for a 
memcg that you do so for all of its children implicitly as well.

But you didn't explain the bahavior in Documenation.

An alternative would be to ensure that a child memcg may never have a 
delay greater than the delay of its parent.  Would you prefer that 
instead?

I don't think such limitation makes sense.

My point is just that the behavior is very special in current memcg interfaces. 
They do
 - It's not allowed to set attribute to no-children, no-parent cgroup

So, please explain above behavior in Documenation.

Thanks,
-Kame


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