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

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Date:	Wed, 19 Aug 2015 20:45:11 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Robin Holt <robinmholt@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	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>, Tony Luck <tony.luck@...el.com>,
	linux-mm@...ck.org, linux-hotplug@...r.kernel.org,
	LKML <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 2015/8/19 19:52, Robin Holt wrote:
> On Sun, Aug 16, 2015 at 10:19 PM, Jiang Liu <jiang.liu@...ux.intel.com> 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);
> 
> I would recommend rejecting this.  First, SGI's UV system does not and
> can not support memory-less nodes.  Additionally the hardware _REALLY_
> wants the memory to be local to the CPU.  We will register this memory
> region with the node firmware.  That will set the hardware up to watch
> this memory block and raise an IRQ targeting the registered CPU when
> anything is written into the memory block.  This is all part of how
> cross-partition communications expects to work.
> 
> Additionally, the interrupt handler will read the memory region, so
> having node-local memory is extremely helpful.
Hi Robin,
	Thanks for review, I will drop this patch in next version.
Actually, if SGI UV systems don't support memoryless node, cpu_to_mem()
is the same as cpu_to_node().
Thanks!
Gerry
> 
> Thanks,
> Robin
> 
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