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

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Message-ID: <20140721200625.GR3935@laptop>
Date:	Mon, 21 Jul 2014 22:06:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tony Luck <tony.luck@...il.com>
Cc:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	"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 Mon, Jul 21, 2014 at 10:41:59AM -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
> Next: Here is some new memory
> 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 we could 'easily' capture that in arch code and make it look
like it was done in a 'sane' order. No need to wreck the rest of the
kernel to support this particular BIOS fuckup.
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