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

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Message-ID: <4B95A379.4000207@cn.fujitsu.com>
Date:	Tue, 09 Mar 2010 09:25:13 +0800
From:	Miao Xie <miaox@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.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 2010-3-9 5:22, David Rientjes wrote:
> 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.

ok, I'll do it.

> 
>> @@ -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.

scan_for_empty_cpusets() will update top_cpuset.mems_allowed when doing MEM_OFFLINE.

The comment of this source is necessary. I'll add it.

Thanks!
Miao

> 
> 


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