Re: [PATCH] ovs: do not allocate memory from offline numa node

[Alexander Duyck]

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@xxxxxxxxxxxxxx>
>
> ...
>
> > 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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