Re: [PATCH v8 1/9] Basic kernel memory functionality for the MemoryController

[Glauber Costa]

On 12/09/2011 12:44 PM, David Laight wrote:
> > How about this?
> >
> >           val = !!val;
> >
> >           /*
> >            * This follows the same hierarchy restrictions than
> >            * mem_cgroup_hierarchy_write()
> >            */
> >           if (!parent || !parent->use_hierarchy) {
> >                   if (list_empty(&cgroup->children))
> >                           memcg->kmem_independent_accounting = val;
> >                   else
> >                           return -EBUSY;
> >           }
> >           else
> >                   return -EINVAL;
> >
> >           return 0;
>
> Inverting the tests gives easier to read code:
>
> 	if (parent&&  parent->user_hierarchy)
> 		return -EINVAL;
> 	if (!list_empty(&cgroup->children))
> 		return -EBUSY;
> 	memcg->kmem_independent_accounting = val != 0;
> 	return 0;

On the other hand, inconsistent with mem_cgroup_hierarchy_write(), which 
applies the logic in the same way I did here.

> NFI about the logic...
> On the face of it the tests don't seem related to each other
> or to the assignment!

How so?

If parent's use_hierarchy is set, we can't set this value (we need to 
have a parent for that to even matter).

We also can't set it if we already have any children - otherwise all the 
on-the-fly adjustments become hell-on-earth.

As for = val != 0, sorry, but I completely disagree this is easier than 
!!val. Not to mention the !!val notation is already pretty widespread in 
the kernel.

> 	David
>
> 	
>
>
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