linux-kernel - Re: [RFC Patch V1 09/30] mm, memcg: Use cpu_to_mem()/numa_mem

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Message-ID: <53CF2977.2040307@linux.intel.com>
Date:	Wed, 23 Jul 2014 11:18:15 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Tony Luck <tony.luck@...el.com>, linux-mm@...ck.org,
	linux-hotplug@...r.kernel.org, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org
Subject: Re: [RFC Patch V1 09/30] mm, memcg: Use cpu_to_mem()/numa_mem_id()
 to support memoryless node

Hi Michal,
	Thanks for your comments! As discussed, we will
rework the patch set in another direction to hide memoryless
node from normal slab users.
Regards!
Gerry

On 2014/7/18 15:36, Michal Hocko wrote:
> On Fri 11-07-14 15:37:26, Jiang Liu wrote:
>> When CONFIG_HAVE_MEMORYLESS_NODES is enabled, cpu_to_node()/numa_node_id()
>> may return a node without memory, and later cause system failure/panic
>> when calling kmalloc_node() and friends with returned node id.
>> So use cpu_to_mem()/numa_mem_id() instead to get the nearest node with
>> memory for the/current cpu.
>>
>> If CONFIG_HAVE_MEMORYLESS_NODES is disabled, cpu_to_mem()/numa_mem_id()
>> is the same as cpu_to_node()/numa_node_id().
> 
> The change makes difference only for really tiny memcgs. If we really
> have all pages on unevictable list or anon with no swap allowed and that
> is the reason why no node is set in scan_nodes mask then reclaiming
> memoryless node or any arbitrary close one doesn't make any difference.
> The current memcg might not have any memory on that node at all.
> 
> So the change doesn't make any practical difference and the changelog is
> misleading.
> 
>> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
>> ---
>>  mm/memcontrol.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index a2c7bcb0e6eb..d6c4b7255ca9 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -1933,7 +1933,7 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
>>  	 * we use curret node.
>>  	 */
>>  	if (unlikely(node == MAX_NUMNODES))
>> -		node = numa_node_id();
>> +		node = numa_mem_id();
>>  
>>  	memcg->last_scanned_node = node;
>>  	return node;
>> -- 
>> 1.7.10.4
>>
> 
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