linux-kernel - RE: [2/8,v3] NUMA Hotplug Emulator: infrastructure of NUMA hotplug emulation

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Message-ID: <789F9655DD1B8F43B48D77C5D30659732FE95E6E@shsmsx501.ccr.corp.intel.com>
Date:	Sun, 21 Nov 2010 23:14:24 +0800
From:	"Li, Haicheng" <haicheng.li@...el.com>
To:	David Rientjes <rientjes@...gle.com>,
	"Zheng, Shaohui" <shaohui.zheng@...el.com>
CC:	Paul Mundt <lethal@...ux-sh.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"haicheng.li@...ux.intel.com" <haicheng.li@...ux.intel.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"shaohui.zheng@...ux.intel.com" <shaohui.zheng@...ux.intel.com>,
	Yinghai Lu <yinghai@...nel.org>
Subject: RE: [2/8,v3] NUMA Hotplug Emulator: infrastructure of NUMA hotplug
 emulation

David Rientjes wrote:
> On Fri, 19 Nov 2010, Shaohui Zheng wrote:
> 
>> nr_node_ids is the possible node number. when we do regular memory
>> online, it is oline to a possible node, and it is already counted in
>> to nr_node_ids. 
>> 
>> if you increment nr_node_ids dynamically when node online, it causes
>> a lot of problems. Many data are initialized according to
>> nr_node_ids. That is our experience when we debug the emulator.
>> 
> 
> I think what we'll end up wanting to do is something like this, which
> adds 
> a numa=possible=<N> parameter for x86; this will add an additional N
> possible nodes to node_possible_map that we can use to online later. 
> It 
> also adds a new /sys/devices/system/memory/add_node file which takes a
> typical "size@...rt" value to hot-add an emulated node.  For example,
> using "mem=2G numa=possible=1" on the command line and doing
> echo 128M@...0000000" > /sys/devices/system/memory/add_node would
> hot-add 
> a node of 128M.
> 
> Comments?

Sorry for the late response as I'm in a biz trip recently.

David, your original concern is just about powerful/flexibility. I'm sure our implementation can better meets such requirments.

IMHO, I don't see any powerful/flexibility from your patch, compared to our original implementation. you just make things more complex and mess.

Why not use "numa=hide=N*size" as originally implemented?
- later you just need to online the node once you want. And it naturally/exactly emulates the behavior that current HW provides.
- N is the possible node number. And we can use 128M as the default size for each hidden node if user doesn't specify a size.
- If user wants more mem for hidden node, he just needs specify the "size".
- besides, user can also use "mem=" to hide more mem and later use mem-add i/f to freely attach more mem to the hidden node during runtime.

Your patch introduces additional dependency on "mem=", but ours is simple and flexibly compatible with "mem=" and "numa=emu". 


-haicheng--
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