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Date: Wed, 23 Dec 2009 11:10:04 +0100
From: Eric Dumazet <eric.dumazet@gmail.com>
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To: Haicheng Li <haicheng.li@linux.intel.com>
CC: Christoph Lameter <cl@linux-foundation.org>, linux-mm@kvack.org,
       Pekka Enberg <penberg@cs.helsinki.fi>, Matt Mackall <mpm@selenic.com>,
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Subject: Re: [PATCH] slab: initialize unused alien cache entry as NULL at
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Le 23/12/2009 07:52, Haicheng Li a écrit :
> Christoph & Matt,
> 
> Thanks for the review. Node ids beyond nr_node_ids could be used in the
> case of
> memory hotadding.
> 
> Let me explain here:
> Firstly, original nr_node_ids = 1 + nid of highest POSSIBLE node.
> 
> Secondly, consider hotplug-adding the memories that are on a new_added
> node:
> 1. when acpi event is triggered:
> acpi_memory_device_add() -> acpi_memory_enable_device() -> add_memory()
> -> node_set_online()
> 
> The node_state[N_ONLINE] is updated with this new node added.
> And the id of this new node is beyond nr_node_ids.
> 

Then, this is a violation of the first statement :

nr_node_ids = 1 + nid of highest POSSIBLE node.

If your system allows hotplugging of new nodes, then POSSIBLE nodes should include them
at boot time.

Same thing for cpus and nr_cpus_ids. If a cpu is added, then its id MUST be < nr_cpus_ids