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Date:	Mon, 17 Feb 2014 11:28:03 -0800
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	David Cohen <david.a.cohen@...ux.intel.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Damien Ramonda <damien.ramonda@...el.com>,
	Jan Kara <jack@...e.cz>, linux-mm <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH V5] mm readahead: Fix readahead fail for no local
 memory and limit readahead pages

On 14.02.2014 [02:54:06 -0800], David Rientjes wrote:
> On Thu, 13 Feb 2014, Nishanth Aravamudan wrote:
> 
> > There is an open issue on powerpc with memoryless nodes (inasmuch as we
> > can have them, but the kernel doesn't support it properly). There is a
> > separate discussion going on on linuxppc-dev about what is necessary for
> > CONFIG_HAVE_MEMORYLESS_NODES to be supported.
> > 
> 
> Yeah, and this is causing problems with the slub allocator as well.
> 
> > Apologies for hijacking the thread, my comments below were purely about
> > the memoryless node support, not about readahead specifically.
> > 
> 
> Neither you nor Raghavendra have any reason to apologize to anybody.  
> Memoryless node support on powerpc isn't working very well right now and 
> you're trying to fix it, that fix is needed both in this thread and in 
> your fixes for slub.  It's great to see both of you working hard on your 
> platform to make it work the best.
> 
> I think what you'll need to do in addition to your 
> CONFIG_HAVE_MEMORYLESS_NODE fix, which is obviously needed, is to enable 
> CONFIG_USE_PERCPU_NUMA_NODE_ID for the same NUMA configurations and then 
> use set_numa_node() or set_cpu_numa_node() to properly store the mapping 
> between cpu and node rather than numa_cpu_lookup_table.  Then you should 
> be able to do away with your own implementation of cpu_to_node().
> 
> After that, I think it should be as simple as doing
> 
> 	set_numa_node(cpu_to_node(cpu));
> 	set_numa_mem(local_memory_node(cpu_to_node(cpu)));
> 
> probably before taking vector_lock in smp_callin().  The cpu-to-node 
> mapping should be done much earlier in boot while the nodes are being 
> initialized, I don't think there should be any problem there.

vector_lock/smp_callin are ia64 specific things, I believe? I think the
equivalent is just in start_secondary() for powerpc? (which in fact is
what calls smp_callin on powerpc).

Here is what I'm running into now:

setup_arch ->
	do_init_bootmem ->
		cpu_numa_callback ->
			numa_setup_cpu ->
				map_cpu_to_node -> 
					update_numa_cpu_lookup_table

Which current updates the powerpc specific numa_cpu_lookup_table. I
would like to update that function to use set_cpu_numa_node() and
set_cpu_numa_mem(), but local_memory_node() is not yet functional
because build_all_zonelists is called later in start_kernel. Would it
make sense for first_zones_zonelist() to return NUMA_NO_NODE if we
don't have a zone?

Thanks,
Nish

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