On Thu 15-12-11 16:29:18, Glauber Costa wrote:

On 12/14/2011 09:04 PM, Michal Hocko wrote:

quoted

[Now with the current patch version, I hope]
On Mon 12-12-11 11:47:01, Glauber Costa wrote:

[...]

quoted

quoted

@@ -3848,10 +3862,17 @@ static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
 	u64 val;

 	if (!mem_cgroup_is_root(memcg)) {
+		val = 0;
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+		if (!memcg->kmem_independent_accounting)
+			val = res_counter_read_u64(&memcg->kmem, RES_USAGE);
+#endif
 		if (!swap)
-			return res_counter_read_u64(&memcg->res, RES_USAGE);
+			val += res_counter_read_u64(&memcg->res, RES_USAGE);
 		else
-			return res_counter_read_u64(&memcg->memsw, RES_USAGE);
+			val += res_counter_read_u64(&memcg->memsw, RES_USAGE);
+
+		return val;
 	}

So you report kmem+user but we do not consider kmem during charge so one
can easily end up with usage_in_bytes over limit but no reclaim is going
on. Not good, I would say.

I find this a problem and one of the reason I do not like !independent
accounting.

quoted

OK, so to sum it up. The biggest problem I see is the (non)independent
accounting. We simply cannot mix user+kernel limits otherwise we would
see issues (like kernel resource hog would force memcg-oom and innocent
members would die because their rss is much bigger).
It is also not clear to me what should happen when we hit the kmem
limit. I guess it will be kmem cache dependent.

So right now, tcp is completely independent, since it is not
accounted to kmem. 

So why do we need kmem accounting when tcp (the only user at the moment)
doesn't use it? 

In summary, we still never do non-independent accounting. When we
start doing it for the other caches, We will have to add a test at
charge time as well.

So we shouldn't do it as a part of this patchset because the further
usage is not clear and I think there will be some real issues with
user+kmem accounting (e.g. a proper memcg-oom implementation).
Can you just drop this patch?

We still need to keep it separate though, in case the independent
flag is turned on/off

I don't mind to have kmem.tcp.* knobs.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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