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

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Message-ID: <alpine.DEB.2.00.1105271628430.9445@chino.kir.corp.google.com>
Date:	Fri, 27 May 2011 16:30:33 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Michal Hocko <mhocko@...e.cz>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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 Sat, 28 May 2011, Michal Hocko wrote:

> > --- 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?
> 

They aren't nodes on UMA machines, they are memory regions for 
DISCONTIGMEM which are separated by large holes in the address space.  
These archs will never sanely use node_random(), so it doesn't really 
matter except for CONFIG_NUMA where MAX_NUMNODES > 1, since they won't be 
selecting random memory regions.
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