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Date:	Wed, 11 Nov 2009 12:04:15 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	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 Tue, 10 Nov 2009 18:49:51 -0800 (PST)
David Rientjes <rientjes@...gle.com> wrote:

> 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.
> 
Hmm, ok, remove.


> >  {
> > -#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.
> 
> 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?
> 

Ah, I didn't notice nodes_subset(). Thank you, I'll use it.


> > +
> > +	/* Check this allocation failure is caused by cpuset's wall function */
> > +	for_each_zone_zonelist_nodemask(zone, z, zonelist,
> > +			high_zoneidx, nodemask)
> > +		if (!cpuset_zone_allowed_softwall(zone, gfp_mask))
> >  			return CONSTRAINT_CPUSET;
> >  
> > -	if (!nodes_empty(nodes))
> > -		return CONSTRAINT_MEMORY_POLICY;
> > -#endif
> > +	/* __GFP_THISNODE never calls OOM.*/
> >  
> >  	return CONSTRAINT_NONE;
> >  }
> > +#else
> > +static inline enum oom_constraint constrained_alloc(struct zonelist *zonelist,
> > +				gfp_t gfp_mask, nodemask_t *nodemask)
> > +{
> > +	return CONSTRAINT_NONE;
> > +}
> > +#endif
> >  
> >  /*
> >   * Simple selection loop. We chose the process with the highest
> > @@ -603,7 +621,8 @@ rest_and_return:
> >   * OR try to be smart about which process to kill. Note that we
> >   * don't have to be perfect here, we just have to be good.
> >   */
> > -void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
> > +void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> > +		int order, nodemask_t *nodemask)
> >  {
> >  	unsigned long freed = 0;
> >  	enum oom_constraint constraint;
> > @@ -622,11 +641,12 @@ void out_of_memory(struct zonelist *zone
> >  	 * Check if there were limitations on the allocation (only relevant for
> >  	 * NUMA) that may require different handling.
> >  	 */
> > -	constraint = constrained_alloc(zonelist, gfp_mask);
> > +	constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
> >  	read_lock(&tasklist_lock);
> >  
> >  	switch (constraint) {
> >  	case CONSTRAINT_MEMORY_POLICY:
> > +		/* kill by process's its own memory alloc limitation */
> 
> I don't understand this comment.
> 
remove this. But it seems not to be well known that current is always killed if
CONSTRAINT_MEMPOLICY. 

> >  		oom_kill_process(current, gfp_mask, order, 0, NULL,
> >  				"No available memory (MPOL_BIND)");
> >  		break;
> > Index: mm-test-kernel/mm/page_alloc.c
> > ===================================================================
> > --- mm-test-kernel.orig/mm/page_alloc.c
> > +++ mm-test-kernel/mm/page_alloc.c
> > @@ -1667,9 +1667,15 @@ __alloc_pages_may_oom(gfp_t gfp_mask, un
> >  	/* The OOM killer will not help higher order allocs */
> >  	if (order > PAGE_ALLOC_COSTLY_ORDER && !(gfp_mask & __GFP_NOFAIL))
> >  		goto out;
> > -
> > +	/*
> > +	 * In usual, GFP_THISNODE contains __GFP_NORETRY and we never hit this.
> > +	 * Sanity check for bare calls of __GFP_THISNODE, not real OOM.
> > +	 * Note: Hugepage uses it but will hit PAGE_ALLOC_COSTLY_ORDER.
> > +	 */
> > +	if (gfp_mask & __GFP_THISNODE)
> > +		goto out;
> >  	/* Exhausted what can be done so it's blamo time */
> > -	out_of_memory(zonelist, gfp_mask, order);
> > +	out_of_memory(zonelist, gfp_mask, order, nodemask);
> >  
> >  out:
> >  	clear_zonelist_oom(zonelist, gfp_mask);
> 
> This doesn't seem like the right place for this check; should we even try 
> direct reclaim for bare users of __GFP_THISNODE?
No, hugepage has to do reclaim.

> If we're adding it for  sanity even though no callers would currently hit it,
> it also is a potential escape route for __GFP_NOFAIL.

will add __GFP_NOFAIL check.

Thanks,
-Kame





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