linux-kernel - Re: [PATCH 7/7] Add /proc/sys/vm/compact_node for the explicit compaction of a node

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Message-ID: <Pine.LNX.4.64.0705292109460.29854@schroedinger.engr.sgi.com>
Date:	Tue, 29 May 2007 21:14:23 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Mel Gorman <mel@....ul.ie>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 7/7] Add /proc/sys/vm/compact_node for the explicit
 compaction of a node

On Tue, 29 May 2007, Mel Gorman wrote:

> +	if (nodeid < 0)
> +		return -EINVAL;
> +
> +	pgdat = NODE_DATA(nodeid);
> +	if (!pgdat || pgdat->node_id != nodeid)
> +		return -EINVAL;

You cannot pass an arbitrary number to node data since NODE_DATA may do a 
simple array lookup.

Check for node < nr_node_ids first.

pgdat->node_id != nodeid? Sounds like something you should BUG() on.

IA64's NODE_DATA is

struct ia64_node_data {
        short                   active_cpu_count;
        short                   node;
        struct pglist_data      *pg_data_ptrs[MAX_NUMNODES];
};

/*
 * Given a node id, return a pointer to the pg_data_t for the node.
 *
 * NODE_DATA    - should be used in all code not related to system
 *                initialization. It uses pernode data structures to minimize
 *                offnode memory references. However, these structure are not
 *                present during boot. This macro can be used once cpu_init
 *                completes.
 */
#define NODE_DATA(nid)          (local_node_data->pg_data_ptrs[nid])

x86_64 also does

#define NODE_DATA(nid)          (node_data[nid])

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