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

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Date:	Mon, 2 Mar 2009 15:18:30 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	linux-mm@...ck.org, Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Bharata B Rao <bharata@...ibm.com>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/4] Memory controller soft limit patches (v3)

On Mon, 2 Mar 2009 11:35:19 +0530
Balbir Singh <balbir@...ux.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.

Thanks,
-Kame

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