linux-kernel - Re: [PATCH v2] cpusets: randomize node rotor used in cpuset_mem_spread

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Message-Id: <20110527142051.d7ec3784.akpm@linux-foundation.org>
Date:	Fri, 27 May 2011 14:20:51 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jack Steiner <steiner@....com>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Paul Menage <menage@...gle.com>, Robin Holt <holt@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-mm@...ck.org
Subject: Re: [PATCH v2] cpusets: randomize node rotor used in
 cpuset_mem_spread_node()

On Fri, 27 May 2011 14:47:05 +0200
Michal Hocko <mhocko@...e.cz> wrote:

> > We use "#if MAX_NUMNODES > 1" in nodemask.h, but we use CONFIG_NUMA
> > when deciding to build mempolicy.o.  That's a bit odd - why didn't
> > nodemask.h use CONFIG_NUMA?
> 
> We have this since the kernel git age. I guess this is just for
> optimizations where some functions can be NOOP when there is only one
> node.
> 
> I know that this is ugly but what if we just define node_random in the
> header?

I think I prefer this:

--- a/include/linux/nodemask.h~cpusets-randomize-node-rotor-used-in-cpuset_mem_spread_node-fix-2
+++ a/include/linux/nodemask.h
@@ -433,8 +433,6 @@ static inline void node_set_offline(int 
 	nr_online_nodes = num_node_state(N_ONLINE);
 }
 
-extern int node_random(const nodemask_t *maskp);
-
 #else
 
 static inline int node_state(int node, enum node_states state)
@@ -466,7 +464,15 @@ static inline int num_node_state(enum no
 #define node_set_online(node)	   node_set_state((node), N_ONLINE)
 #define node_set_offline(node)	   node_clear_state((node), N_ONLINE)
 
-static inline int node_random(const nodemask_t *mask) { return 0; }
+#endif
+
+#if defined(CONFIG_NUMA) && (MAX_NUMNODES > 1)
+extern int node_random(const nodemask_t *maskp);
+#else
+static inline int node_random(const nodemask_t *mask)
+{
+	return 0;
+}
 #endif
 
 #define node_online_map 	node_states[N_ONLINE]


It's beyond weird that we implement node_random() if
defined(CONFIG_NUMA) && (MAX_NUMNODES > 1), and only use it if
defined(CONFIG_CPUSETS).
--
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