Glauber Costa Messages: 916 Registered: October 2011
Senior Member
On 06/25/2012 10:29 PM, Tejun Heo wrote:
> Feeling like a nit pervert but..
>
> On Mon, Jun 25, 2012 at 06:15:26PM +0400, Glauber Costa wrote:
>> @@ -287,7 +287,11 @@ struct mem_cgroup {
>> * Should the accounting and control be hierarchical, per subtree?
>> */
>> bool use_hierarchy;
>> - bool kmem_accounted;
>> + /*
>> + * bit0: accounted by this cgroup
>> + * bit1: accounted by a parent.
>> + */
>> + volatile unsigned long kmem_accounted;
>
> Is the volatile declaration really necessary? Why is it necessary?
> Why no comment explaining it?
Seems to be required by set_bit and friends. gcc will complain if it is
not volatile (take a look at the bit function headers)
>> +
>> + for_each_mem_cgroup_tree(iter, memcg) {
>> + struct mem_cgroup *parent;
>
> Blank line between decl and body please.
ok.
>
>> + 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?
I can simplify to test parent != memcg only, indeed it is not expected
to be NULL (but if it happens to be due to any kind of bug, we protect
against NULL-dereference, that is why I like to write this way)
>> + 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.
>
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