Re: [PATCH v5 14/14] memory-hotplug: free node_data when a node is offlined
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- To: Wen Congyang <wency@xxxxxxxxxxxxxx>
- Subject: Re: [PATCH v5 14/14] memory-hotplug: free node_data when a node is offlined
- From: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
- Date: Mon, 07 Jan 2013 14:30:37 +0900
- Cc: Tang Chen <tangchen@xxxxxxxxxxxxxx>, akpm@xxxxxxxxxxxxxxxxxxxx, rientjes@xxxxxxxxxx, liuj97@xxxxxxxxx, len.brown@xxxxxxxxx, benh@xxxxxxxxxxxxxxxxxxx, paulus@xxxxxxxxx, cl@xxxxxxxxx, minchan.kim@xxxxxxxxx, kosaki.motohiro@xxxxxxxxxxxxxx, isimatu.yasuaki@xxxxxxxxxxxxxx, wujianguo@xxxxxxxxxx, hpa@xxxxxxxxx, linfeng@xxxxxxxxxxxxxx, laijs@xxxxxxxxxxxxxx, mgorman@xxxxxxx, yinghai@xxxxxxxxxx, x86@xxxxxxxxxx, linux-mm@xxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linuxppc-dev@xxxxxxxxxxxxxxxx, linux-acpi@xxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, cmetcalf@xxxxxxxxxx, sparclinux@xxxxxxxxxxxxxxx
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(2012/12/30 15:02), Wen Congyang wrote:
> At 12/28/2012 08:28 AM, Kamezawa Hiroyuki Wrote:
>> (2012/12/27 21:16), Wen Congyang wrote:
>>> At 12/26/2012 11:55 AM, Kamezawa Hiroyuki Wrote:
>>>> (2012/12/24 21:09), Tang Chen wrote:
>>>>> From: Wen Congyang <wency@xxxxxxxxxxxxxx>
>>>>>
>>>>> We call hotadd_new_pgdat() to allocate memory to store node_data. So we
>>>>> should free it when removing a node.
>>>>>
>>>>> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
>>>>
>>>> I'm sorry but is it safe to remove pgdat ? All zone cache and zonelists are
>>>> properly cleared/rebuilded in synchronous way ? and No threads are visinting
>>>> zone in vmscan.c ?
>>>
>>> We have rebuilt zonelists when a zone has no memory after offlining some pages.
>>>
>>
>> How do you guarantee that the address of pgdat/zone is not on stack of any kernel
>> threads or other kernel objects without reference counting or other syncing method ?
>
> No way to guarentee this. But, the kernel should not use the address of pgdat/zone when
> it is offlined.
>
> Hmm, what about this: reuse the memory when the node is onlined again?
>
That's the only way which we can go now. Please don't free it.
Thanks,
-Kame
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