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

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Date:	Sat, 28 May 2011 01:17:00 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 27-05-11 14:20:51, Andrew Morton wrote:
> 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

I have to admit that I quite don't understand concept of several nodes
with UMA archs but do we really want to provide the sane node all the
time?

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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