linux-kernel - Re: [PATCH 21/22] Use a pre-calculated value instead of num_online

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Date:	Thu, 23 Apr 2009 12:29:27 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Mel Gorman <mel@....ul.ie>
cc:	Linux Memory Management List <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 21/22] Use a pre-calculated value instead of num_online_nodes()
 in fast paths

On Thu, 23 Apr 2009, Mel Gorman wrote:

> > > diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
> > > index 848025c..474e73e 100644
> > > --- a/include/linux/nodemask.h
> > > +++ b/include/linux/nodemask.h
> > > @@ -408,6 +408,19 @@ static inline int num_node_state(enum node_states state)
> > >  #define next_online_node(nid)	next_node((nid), node_states[N_ONLINE])
> > >  
> > >  extern int nr_node_ids;
> > > +extern int nr_online_nodes;
> > > +
> > > +static inline void node_set_online(int nid)
> > > +{
> > > +	node_set_state(nid, N_ONLINE);
> > > +	nr_online_nodes = num_node_state(N_ONLINE);
> > > +}
> > > +
> > > +static inline void node_set_offline(int nid)
> > > +{
> > > +	node_clear_state(nid, N_ONLINE);
> > > +	nr_online_nodes = num_node_state(N_ONLINE);
> > > +}
> > >  #else
> > >  
> > >  static inline int node_state(int node, enum node_states state)
> > 
> > The later #define's of node_set_online() and node_set_offline() in 
> > include/linux/nodemask.h should probably be removed now.
> > 
> 
> You'd think, but you can enable memory hotplug without NUMA and
> node_set_online() is called when adding memory. Even though those
> functions are nops on !NUMA, they're necessary.
> 

The problem is that your new functions above are never used because 
node_set_online and node_set_offline are macro defined later in this 
header for all cases, not just !CONFIG_NUMA.

You need this.
---
diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
--- a/include/linux/nodemask.h
+++ b/include/linux/nodemask.h
@@ -448,6 +448,9 @@ static inline int num_node_state(enum node_states state)
 #define next_online_node(nid)	(MAX_NUMNODES)
 #define nr_node_ids		1
 #define nr_online_nodes		1
+
+#define node_set_online(node)	   node_set_state((node), N_ONLINE)
+#define node_set_offline(node)	   node_clear_state((node), N_ONLINE)
 #endif
 
 #define node_online_map 	node_states[N_ONLINE]
@@ -467,9 +470,6 @@ static inline int num_node_state(enum node_states state)
 #define node_online(node)	node_state((node), N_ONLINE)
 #define node_possible(node)	node_state((node), N_POSSIBLE)
 
-#define node_set_online(node)	   node_set_state((node), N_ONLINE)
-#define node_set_offline(node)	   node_clear_state((node), N_ONLINE)
-
 #define for_each_node(node)	   for_each_node_state(node, N_POSSIBLE)
 #define for_each_online_node(node) for_each_node_state(node, N_ONLINE)
 
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