linux-kernel - Re: [PATCH] online CPU before memory failed in pcpu_alloc

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Date:	Fri, 21 May 2010 16:22:19 +0800
From:	minskey guo <chaohong_guo@...ux.intel.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	prarit@...hat.com, andi.kleen@...el.com,
	linux-kernel@...r.kernel.org, minskey guo <chaohong.guo@...el.com>,
	Tejun Heo <tj@...nel.org>, stable@...nel.org
Subject: Re: [PATCH] online CPU before memory failed in pcpu_alloc_pages()


>>>> --- a/mm/percpu.c
>>>> +++ b/mm/percpu.c
>>>> @@ -714,13 +714,29 @@ static int pcpu_alloc_pages(struct pcpu_chunk *chunk,
>>>
>>> In linux-next, Tejun has gone and moved pcpu_alloc_pages() into the new
>>> mm/percpu-vm.c.  So either
>>
>> This has gone into Linus' tree today ...
>>
>
> Hmm, a comment here.
>
> Recently, Lee Schermerhorn developed
>
>   numa-introduce-numa_mem_id-effective-local-memory-node-id-fix2.patch
>
> Then, you can use cpu_to_mem() instead of cpu_to_node() to find the
> nearest available node.
> I don't check cpu_to_mem() is synchronized with NUMA hotplug but
> using cpu_to_mem() rather than adding
> =
>
> +			if ((nid == -1) ||
> +			    !(node_zonelist(nid, GFP_KERNEL)->_zonerefs->zone))
> +				nid = numa_node_id();
> +
> ==
>
> is better.


Yes.  I can use cpu_to_mem().  only some little difference during
CPU online:  1st cpu within memoryless node gets memory from current
node or the node to which the cpu0 belongs,


But I have a question about the patch:

    numa-slab-use-numa_mem_id-for-slab-local-memory-node.patch,




@@ -2968,9 +2991,23 @@ static int __build_all_zonelists(void *d
...

-	for_each_possible_cpu(cpu)
+	for_each_possible_cpu(cpu) {
		setup_pageset(&per_cpu(boot_pageset, cpu), 0);
...

+#ifdef CONFIG_HAVE_MEMORYLESS_NODES
+ 	if (cpu_online(cpu))
+		cpu_to_mem(cpu) = local_memory_node(cpu_to_node(cpu));
+#endif


Look at the last two lines, suppose that memory is onlined before CPUs,
where will cpu_to_mem(cpu) be set to the right nodeid for the last
onlined cpu ?  Does that CPU always get memory from the node including 
cpu0 for slab allocator where cpu_to_mem() is used ?



thanks,
-minskey



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