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

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Date:	Thu, 24 Jul 2014 16:32:30 -0700
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
Cc:	Tony Luck <tony.luck@...il.com>,
	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 23.07.2014 [16:20:24 +0800], Jiang Liu wrote:
> 
> 
> 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.

Ok, it seems like you have two sets of patches then? One is to fix the
NUMA information timing (30/30 only). The rest of the patches are
general discussions about where cpu_to_mem() might be used instead of
cpu_to_node(). However, based upon Tejun's feedback, it seems like
rather than force all callers to use cpu_to_mem(), we should be looking
at the core VM to ensure fallback is occuring appropriately when
memoryless nodes are present. 

Do you have a specific situation, once you've applied 30/30, where
kmalloc_node() leads to an Oops?

Thanks,
Nish

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