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

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Message-ID: <CF2F38D4AE21BB4CB845318E4C5ECB671E790AF3@shsmsx501.ccr.corp.intel.com>
Date:	Tue, 25 May 2010 09:35:27 +0800
From:	"Guo, Chaohong" <chaohong.guo@...el.com>
To:	Lee Schermerhorn <Lee.Schermerhorn@...com>
CC:	minskey guo <chaohong_guo@...ux.intel.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"prarit@...hat.com" <prarit@...hat.com>,
	"Kleen, Andi" <andi.kleen@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	"stable@...nel.org" <stable@...nel.org>
Subject: RE: [PATCH] online CPU before memory failed in pcpu_alloc_pages()



>>
>>  But currently, I don't
>> >think you can use the numa_mem_id()/cpu_to_mem() interfaces for your
>> >purpose.  I suppose you could change page_alloc.c to compile
>> >local_memory_node() #if defined(CONFIG_HAVE_MEMORYLESS_NODES) ||
>> >defined
>> >(CPU_HOTPLUG) and use that function to find the nearest memory.  It
>> >should return a valid node after zonelists have been rebuilt.
>> >
>> >Does that make sense?
>>
>> Yes, besides,  I need to find a place in hotplug path to call set_numa_mem()
>> just as you mentioned for ia64 platform.  Is my understanding right ?
>
>I don't think you can use any of the "numa_mem" functions on x86[_64]
>without doing a lot more work to expose memoryless nodes.  On x86_64,
>numa_mem_id() and cpu_to_mem() always return the same as numa_node_id()
>and cpu_to_node().  This is because x86_64 code hides memoryless nodes
>and reassigns all cpus to nodes with memory.  Are you planning on
>changing this such that memoryless nodes remain on-line with their cpus
>associated with them?  If so, go for it!   If not, then you don't need
>to [can't really, I think] use set_numa_mem()/cpu_to_mem() for your
>purposes.  That's why I suggested you arrange for local_memory_node() to
>be compiled for CPU_HOTPLUG and call that function directly to obtain a
>nearby node from which you can allocate memory during cpu hot plug.  Or,
>I could just completely misunderstand what you propose to do with these
>percpu variables.

Got it, thank you very much for detailed explanation.


-minskey
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