linux-kernel - Re: [RFC Patch V1 00/30] Enable memoryless node on x86 platforms

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Date:	Wed, 23 Jul 2014 16:20:24 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>,
	Tony Luck <tony.luck@...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>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-hotplug@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC Patch V1 00/30] Enable memoryless node on x86 platforms



On 2014/7/22 1:57, Nishanth Aravamudan wrote:
> On 21.07.2014 [10:41:59 -0700], Tony Luck wrote:
>> On Mon, Jul 21, 2014 at 10:23 AM, Nishanth Aravamudan
>> <nacc@...ux.vnet.ibm.com> wrote:
>>> It seems like the issue is the order of onlining of resources on a
>>> specific x86 platform?
>>
>> Yes. When we online a node the BIOS hits us with some ACPI hotplug events:
>>
>> First: Here are some new cpus
> 
> Ok, so during this period, you might get some remote allocations. Do you
> know the topology of these CPUs? That is they belong to a
> (soon-to-exist) NUMA node? Can you online that currently offline NUMA
> node at this point (so that NODE_DATA()) resolves, etc.)?
Hi Nishanth,
	We have method to get the NUMA information about the CPU, and
patch "[RFC Patch V1 30/30] x86, NUMA: Online node earlier when doing
CPU hot-addition" tries to solve this issue by onlining NUMA node
as early as possible. Actually we are trying to enable memoryless node
as you have suggested.

Regards!
Gerry

> 
>> Next: Here is some new memory
> 
> And then update the NUMA topology at this point? That is,
> set_cpu_numa_node/mem as appropriate so the underlying allocators do the
> right thing?
> 
>> Last; Here are some new I/O things (PCIe root ports, PCIe devices,
>> IOAPICs, IOMMUs, ...)
>>
>> So there is a period where the node is memoryless - although that will
>> generally be resolved when the memory hot plug event arrives ... that
>> isn't guaranteed to occur (there might not be any memory on the node,
>> or what memory there is may have failed self-test and been disabled).
> 
> Right, but the allocator(s) generally does the right thing already in
> the face of memoryless nodes -- they fallback to the nearest node. That
> leads to poor performance, but is functional. Based upon the previous
> thread Jiang pointed to, it seems like the real issue here isn't that
> the node is memoryless, but that it's not even online yet? So NODE_DATA
> access crashes?
> 
> Thanks,
> Nish
> 
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