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Date:	Wed, 11 Nov 2009 12:23:43 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [BUGFIX][PATCH] oom-kill: fix NUMA consraint check with nodemask v3

> On Wed, 11 Nov 2009, KOSAKI Motohiro wrote:
> 
> > > >  {
> > > > -#ifdef CONFIG_NUMA
> > > >  	struct zone *zone;
> > > >  	struct zoneref *z;
> > > >  	enum zone_type high_zoneidx = gfp_zone(gfp_mask);
> > > > -	nodemask_t nodes = node_states[N_HIGH_MEMORY];
> > > > +	int ret = CONSTRAINT_NONE;
> > > >  
> > > > -	for_each_zone_zonelist(zone, z, zonelist, high_zoneidx)
> > > > -		if (cpuset_zone_allowed_softwall(zone, gfp_mask))
> > > > -			node_clear(zone_to_nid(zone), nodes);
> > > > -		else
> > > > +	/*
> > > > + 	 * The nodemask here is a nodemask passed to alloc_pages(). Now,
> > > > + 	 * cpuset doesn't use this nodemask for its hardwall/softwall/hierarchy
> > > > + 	 * feature. mempolicy is an only user of nodemask here.
> > > > + 	 */
> > > > +	if (nodemask) {
> > > > +		nodemask_t mask;
> > > > +		/* check mempolicy's nodemask contains all N_HIGH_MEMORY */
> > > > +		nodes_and(mask, *nodemask, node_states[N_HIGH_MEMORY]);
> > > > +		if (!nodes_equal(mask, node_states[N_HIGH_MEMORY]))
> > > > +			return CONSTRAINT_MEMORY_POLICY;
> > > > +	}
> > > 
> > > Although a nodemask_t was previously allocated on the stack, we should 
> > > probably change this to use NODEMASK_ALLOC() for kernels with higher 
> > > CONFIG_NODES_SHIFT since allocations can happen very deep into the stack.
> > 
> > No. NODEMASK_ALLOC() is crap. we should remove it. 
> 
> I've booted 1K node systems and have found it to be helpful to ensure that 
> the stack will not overflow especially in areas where we normally are deep 
> already, such as in the page allocator.

Linux doesn't support 1K nodes. (and only SGI huge machine use 512 nodes)

At least, NODEMASK_ALLOC should make more cleaner interface. current one
and struct nodemask_scratch are pretty ugly.


> > btw, CPUMASK_ALLOC was already removed.
> 
> I don't remember CPUMASK_ALLOC() actually being merged.  I know the 
> comment exists in nodemask.h, but I don't recall any CPUMASK_ALLOC() users 
> in the tree.



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