Feeling like a nit pervert but..

On Mon, Jun 25, 2012 at 06:15:26PM +0400, Glauber Costa wrote:

Is the volatile declaration really necessary?  Why is it necessary?
Why no comment explaining it?

+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+static void mem_cgroup_update_kmem_limit(struct mem_cgroup *memcg, u64 val)
+{
+	struct mem_cgroup *iter;
+
+	mutex_lock(&set_limit_mutex);
+	if (!test_and_set_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted) &&
+		val != RESOURCE_MAX) {
+
+		/*
+		 * Once enabled, can't be disabled. We could in theory
+		 * disable it if we haven't yet created any caches, or
+		 * if we can shrink them all to death.
+		 *
+		 * But it is not worth the trouble
+		 */
+		static_key_slow_inc(&mem_cgroup_kmem_enabled_key);
+
+		if (!memcg->use_hierarchy)
+			goto out;
+
+		for_each_mem_cgroup_tree(iter, memcg) {
+			if (iter == memcg)
+				continue;
+			set_bit(KMEM_ACCOUNTED_PARENT, &iter->kmem_accounted);
+		}
+
+	} else if (test_and_clear_bit(KMEM_ACCOUNTED_THIS, &memcg->kmem_accounted)
+		&& val == RESOURCE_MAX) {
+
+		if (!memcg->use_hierarchy)
+			goto out;
+
+		for_each_mem_cgroup_tree(iter, memcg) {
+			struct mem_cgroup *parent;

Blank line between decl and body please.

+			if (iter == memcg)
+				continue;
+			/*
+			 * We should only have our parent bit cleared if none of
+			 * ouri parents are accounted. The transversal order of

                              ^ type

+			 * our iter function forces us to always look at the
+			 * parents.

Also, it's okay here but the text filling in comments and patch
descriptions tend to be quite inconsistent.  If you're on emacs, alt-q
is your friend and I'm sure vim can do text filling pretty nicely too.

+			 */
+			parent = parent_mem_cgroup(iter);
+			while (parent && (parent != memcg)) {
+				if (test_bit(KMEM_ACCOUNTED_THIS, &parent->kmem_accounted))
+					goto noclear;
+					
+				parent = parent_mem_cgroup(parent);
+			}

Better written in for (;;)?  Also, if we're breaking on parent ==
memcg, can we ever hit NULL parent in the above loop?

+			clear_bit(KMEM_ACCOUNTED_PARENT, &iter->kmem_accounted);
+noclear:
+			continue;
+		}
+	}
+out:
+	mutex_unlock(&set_limit_mutex);

Can we please branch on val != RECOURSE_MAX first?  I'm not even sure
whether the above conditionals are correct.  If the user updates an
existing kmem limit, the first test_and_set_bit() returns non-zero, so
the code proceeds onto clearing KMEM_ACCOUNTED_THIS, which succeeds
but val == RESOURCE_MAX fails so it doesn't do anything.  If the user
changes it again, it will set ACCOUNTED_THIS again.  So, changing an
existing kmem limit toggles KMEM_ACCOUNTED_THIS, which just seems
wacky to me.

Thanks.

-- 
tejun

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