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Subject: Re: [PATCH] ovs: do not allocate memory from offline numa node
References: <20151002101822.12499.27658.stgit@buzz> <56128238.8010305@suse.cz>
From: Alexander Duyck <alexander.duyck@gmail.com>
Message-ID: <5612DCC8.4040605@gmail.com>
Date: Mon, 5 Oct 2015 13:25:44 -0700
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To: Vlastimil Babka <vbabka@suse.cz>, Konstantin Khlebnikov <khlebnikov@yandex-team.ru>, dev@openvswitch.org, Pravin Shelar <pshelar@nicira.com>, "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org

On 10/05/2015 06:59 AM, Vlastimil Babka wrote:
> On 10/02/2015 12:18 PM, Konstantin Khlebnikov wrote:
>> When openvswitch tries allocate memory from offline numa node 0:
>> stats = kmem_cache_alloc_node(flow_stats_cache, GFP_KERNEL | 
>> __GFP_ZERO, 0)
>> It catches VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES || 
>> !node_online(nid))
>> [ replaced with VM_WARN_ON(!node_online(nid)) recently ] in linux/gfp.h
>> This patch disables numa affinity in this case.
>>
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>
> ...
>
>> diff --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c
>> index f2ea83ba4763..c7f74aab34b9 100644
>> --- a/net/openvswitch/flow_table.c
>> +++ b/net/openvswitch/flow_table.c
>> @@ -93,7 +93,8 @@ struct sw_flow *ovs_flow_alloc(void)
>>
>>       /* Initialize the default stat node. */
>>       stats = kmem_cache_alloc_node(flow_stats_cache,
>> -                      GFP_KERNEL | __GFP_ZERO, 0);
>> +                      GFP_KERNEL | __GFP_ZERO,
>> +                      node_online(0) ? 0 : NUMA_NO_NODE);
>
> Stupid question: can node 0 become offline between this check, and the 
> VM_WARN_ON? :) BTW what kind of system has node 0 offline?

Another question to ask would be is it possible for node 0 to be online, 
but be a memoryless node?

I would say you are better off just making this call kmem_cache_alloc.  
I don't see anything that indicates the memory has to come from node 0, 
so adding the extra overhead doesn't provide any value.

- Alex

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