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

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Date:	Fri, 24 Jul 2015 10:48:39 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Vlastimil Babka <vbabka@...e.cz>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	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, 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?

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