linux-kernel - Re: [PATCH V2 1/4] cpuset: fix the problem that cpuset_mem_spread

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Message-ID: <alpine.DEB.2.00.1003081318460.14689@chino.kir.corp.google.com>
Date:	Mon, 8 Mar 2010 13:22:38 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Miao Xie <miaox@...fujitsu.com>
cc:	Lee Schermerhorn <lee.schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>, Paul Menage <menage@...gle.com>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH V2 1/4] cpuset: fix the problem that cpuset_mem_spread_node()
 returns an offline node

On Mon, 8 Mar 2010, Miao Xie wrote:

> Changes from V1 to V2:
> - cleanup two unnecessary smp_wmb() at cpuset_migrate_mm()
> 

This patch is already in -mm without this update, so it's probably better 
to make this an incremental series basedo n mmotm-2010-03-04-18-05 or 
later.

> @@ -2090,15 +2086,19 @@ static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
>  static int cpuset_track_online_nodes(struct notifier_block *self,
>  				unsigned long action, void *arg)
>  {
> +	nodemask_t oldmems;
> +
>  	cgroup_lock();
>  	switch (action) {
>  	case MEM_ONLINE:
> -	case MEM_OFFLINE:
> +		oldmems = top_cpuset.mems_allowed;
>  		mutex_lock(&callback_mutex);
>  		top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
>  		mutex_unlock(&callback_mutex);
> -		if (action == MEM_OFFLINE)
> -			scan_for_empty_cpusets(&top_cpuset);
> +		update_tasks_nodemask(&top_cpuset, &oldmems, NULL);
> +		break;
> +	case MEM_OFFLINE:
> +		scan_for_empty_cpusets(&top_cpuset);
>  		break;
>  	default:
>  		break;

This looks wrong, why isn't top_cpuset.mems_allowed updated for 
MEM_OFFLINE?  If you're going to update it when a new node comes online 
for (struct memory_notify *)arg->status_change_nid is >= 0, then it should 
be removed from the nodemask when offlined as well.  You'd be calling 
scan_for_empty_cpusets() needlessly in this code since it'll never change 
under your hotplug code.
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