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Date:	Wed, 11 Nov 2009 12:02:06 +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

Hi

> On Wed, 11 Nov 2009, KAMEZAWA Hiroyuki wrote:
> 
> > Index: mm-test-kernel/drivers/char/sysrq.c
> > ===================================================================
> > --- mm-test-kernel.orig/drivers/char/sysrq.c
> > +++ mm-test-kernel/drivers/char/sysrq.c
> > @@ -339,7 +339,7 @@ static struct sysrq_key_op sysrq_term_op
> >  
> >  static void moom_callback(struct work_struct *ignored)
> >  {
> > -	out_of_memory(node_zonelist(0, GFP_KERNEL), GFP_KERNEL, 0);
> > +	out_of_memory(node_zonelist(0, GFP_KERNEL), GFP_KERNEL, 0, NULL);
> >  }
> >  
> >  static DECLARE_WORK(moom_work, moom_callback);
> > Index: mm-test-kernel/mm/oom_kill.c
> > ===================================================================
> > --- mm-test-kernel.orig/mm/oom_kill.c
> > +++ mm-test-kernel/mm/oom_kill.c
> > @@ -196,27 +196,45 @@ unsigned long badness(struct task_struct
> >  /*
> >   * Determine the type of allocation constraint.
> >   */
> > +#ifdef CONFIG_NUMA
> >  static inline enum oom_constraint constrained_alloc(struct zonelist *zonelist,
> > -						    gfp_t gfp_mask)
> > +				    gfp_t gfp_mask, nodemask_t *nodemask)
> 
> We should probably remove the inline specifier, there's only one caller 
> currently and if additional ones were added in the future this function 
> should probably not be replicated.

Good catch.


> >  {
> > -#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. 
btw, CPUMASK_ALLOC was already removed.


> There should be a way around that, however.  Shouldn't
> 
> 	if (nodes_subset(node_states[N_HIGH_MEMORY], *nodemask))
> 		return CONSTRAINT_MEMORY_POLICY;
> 
> be sufficient?

Is this safe on memory hotplug case?




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