linux-kernel - Re: [Patch V3 3/9] sgi-xp: Replace cpu_to_node() with cpu_to

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Date:	Mon, 17 Aug 2015 17:25:15 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Tang Chen <tangchen@...fujitsu.com>, Tejun Heo <tj@...nel.org>,
	Cliff Whickman <cpw@....com>,
	Robin Holt <robinmholt@...il.com>,
	Tony Luck <tony.luck@...el.com>, linux-mm@...ck.org,
	linux-hotplug@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [Patch V3 3/9] sgi-xp: Replace cpu_to_node() with cpu_to_mem()
 to support memoryless node

On Mon, 17 Aug 2015, Jiang Liu wrote:

> Function xpc_create_gru_mq_uv() allocates memory with __GFP_THISNODE
> flag set, which may cause permanent memory allocation failure on
> memoryless node. So replace cpu_to_node() with cpu_to_mem() to better
> support memoryless node. For node with memory, cpu_to_mem() is the same
> as cpu_to_node().
> 
> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
> ---
>  drivers/misc/sgi-xp/xpc_uv.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/sgi-xp/xpc_uv.c b/drivers/misc/sgi-xp/xpc_uv.c
> index 95c894482fdd..9210981c0d5b 100644
> --- a/drivers/misc/sgi-xp/xpc_uv.c
> +++ b/drivers/misc/sgi-xp/xpc_uv.c
> @@ -238,7 +238,7 @@ xpc_create_gru_mq_uv(unsigned int mq_size, int cpu, char *irq_name,
>  
>  	mq->mmr_blade = uv_cpu_to_blade_id(cpu);
>  
> -	nid = cpu_to_node(cpu);
> +	nid = cpu_to_mem(cpu);
>  	page = alloc_pages_exact_node(nid,
>  				      GFP_KERNEL | __GFP_ZERO | __GFP_THISNODE,
>  				      pg_order);

Why not simply fix build_zonelists_node() so that the __GFP_THISNODE 
zonelists are set up to reference the zones of cpu_to_mem() for memoryless 
nodes?

It seems much better than checking and maintaining every __GFP_THISNODE 
user to determine if they are using a memoryless node or not.  I don't 
feel that this solution is maintainable in the longterm.
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