linux-kernel - Re: [RFC, 3/7] NUMA hotplug emulator

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Message-ID: <4BECB1CB.2030802@linux.intel.com>
Date:	Fri, 14 May 2010 10:13:31 +0800
From:	Haicheng Li <haicheng.li@...ux.intel.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	Greg KH <gregkh@...e.de>, akpm@...ux-foundation.org,
	linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Alex Chiang <achiang@...com>, linux-kernel@...r.kernel.org,
	ak@...ux.intel.com, fengguang.wu@...el.com,
	shaohui.zheng@...ux.intel.com
Subject: Re: [RFC, 3/7] NUMA hotplug emulator

Dave Hansen wrote:
> On Thu, 2010-05-13 at 09:55 -0700, Greg KH wrote:
>>> Add a sysfs entry "probe" under /sys/devices/system/node/:
>>>
>>>  - to show all fake offlined nodes:
>>>     $ cat /sys/devices/system/node/probe
>>>
>>>  - to hotadd a fake offlined node, e.g. nodeid is N:
>>>     $ echo N > /sys/devices/system/node/probe
>> As you are trying to add a new sysfs file, please create the matching
>> Documentation/ABI/ file as well.
>>
>> Also note that sysfs files are "one value per file", which I don't think
>> this file follows, right?
> 
> I think in this case, it was meant to be a list of acceptable parameters
> rather than a set of values, kinda like /sys/power/state.

Right.

> Instead, I guess we could have:
> 
> 	/sys/devices/system/node/probeable/3
> 	/sys/devices/system/node/probeable/43
> 	/sys/devices/system/node/probeable/65
> 	/sys/devices/system/node/probeable/5145
> 
> and the knowledge that you need to pick one of those to echo
> into /sys/devices/system/node/probe.

I think this way would make things complex if we just want to show user which node could be hotadded.

>  But, it's a lot more self
> explanatory if you 'cat /sys/devices/system/node/probe', and then pick
> one of those to echo back into the file.

agreed.

> Seems like a decent place to violate the "rule". :)



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