linux-kernel - Re: [RFC v2 4/4] mm: fallback for offline nodes in alloc_pages

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Date:	Fri, 24 Jul 2015 12:54:32 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux.com>
cc:	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Greg Thelen <gthelen@...gle.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Subject: Re: [RFC v2 4/4] mm: fallback for offline nodes in
 alloc_pages_node

On Fri, 24 Jul 2015, Christoph Lameter wrote:

> On Fri, 24 Jul 2015, Vlastimil Babka wrote:
> 
> > diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> > index 531c72d..104a027 100644
> > --- a/include/linux/gfp.h
> > +++ b/include/linux/gfp.h
> > @@ -321,8 +321,12 @@ static inline struct page *alloc_pages_node(int nid, gfp_t gfp_mask,
> >  						unsigned int order)
> >  {
> >  	/* Unknown node is current (or closest) node */
> > -	if (nid == NUMA_NO_NODE)
> > +	if (nid == NUMA_NO_NODE) {
> >  		nid = numa_mem_id();
> > +	} else if (!node_online(nid)) {
> > +		VM_WARN_ON(!node_online(nid));
> > +		nid = numa_mem_id();
> > +	}
> 
> I would think you would only want this for debugging purposes. The
> overwhelming majority of hardware out there has no memory
> onlining/offlining capability after all and this adds the overhead to each
> call to alloc_pages_node.
> 
> Make this dependo n CONFIG_VM_DEBUG or some such thing?
> 

Yeah, the suggestion was for VM_WARN_ON() in the conditional, but the 
placement has changed somewhat because of the new __alloc_pages_node().  I 
think

	else if (VM_WARN_ON(!node_online(nid)))
		nid = numa_mem_id();

should be fine since it only triggers for CONFIG_DEBUG_VM.
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