Re: [PATCH 0/4] Memory controller soft limit patches (v3)

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-03-02 15:18:30]:

> On Mon, 2 Mar 2009 11:35:19 +0530
> Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> 
> > > Then, not-sorted RB-tree can be there.
> > > 
> > > BTW,
> > >    time_after(jiffies, 0)
> > > is buggy (see definition). If you want make this true always,
> > >    time_after(jiffies, jiffies +1)
> > >
> > 
> > HZ/4 is 250/4 jiffies in the worst case (62). We have
> > time_after(jiffies, next_update_interval) and next_update_interval is
> > set to last_tree_update + 62. Not sure if I got what you are pointing
> > to.
> > 
> +	unsigned long next_update = 0;
> +	unsigned long flags;
> +
> +	if (!css_tryget(&mem->css))
> +		return;
> +	prev_usage_in_excess = mem->usage_in_excess;
> +	new_usage_in_excess = res_counter_soft_limit_excess(&mem->res);
> +
> +	if (time_check)
> +		next_update = mem->last_tree_update +
> +				MEM_CGROUP_TREE_UPDATE_INTERVAL;
> +	if (new_usage_in_excess && time_after(jiffies, next_update)) {
> +		if (prev_usage_in_excess)
> +			mem_cgroup_remove_exceeded(mem);
> +		mem_cgroup_insert_exceeded(mem);
> +		updated_tree = true;
> +	} else if (prev_usage_in_excess && !new_usage_in_excess) {
> +		mem_cgroup_remove_exceeded(mem);
> +		updated_tree = true;
> +	}
> 
> My point is what happens if time_check==false.
> time_afrter(jiffies, 0) is buggy.
>

I see your point now, but the idea behind doing so is that
time_after(jiffies, 0) will always return false, which forces the
prev_usage_in_excess and !new_usage_in_excess check to execute. We set
the value to false only from __mem_cgroup_free().

Are you suggesting that calling time_after(jiffies, 0) is buggy?
The comment

  Do this with "<0" and ">=0" to only test the sign of the result. A
 
I think refers to the comparison check and not to the parameters. I
hope I am reading this right.
-- 
	Balbir