linux-kernel - Re: sched: CPU #1's llc-sibling CPU #0 is not on the same node!

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Message-ID: <CAE9FiQV9JRk1SYLkBXsQmrSEDHrYZDpBV6UZb+U5rB7=4gFhVA@mail.gmail.com>
Date:	Tue, 26 Feb 2013 22:54:38 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Tang Chen <tangchen@...fujitsu.com>,
	Don Morris <don.morris@...com>,
	Tim Gardner <tim.gardner@...onical.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Tony Luck <tony.luck@...el.com>,
	Thomas Renninger <trenn@...e.de>, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	jarkko.sakkinen@...el.com
Subject: Re: sched: CPU #1's llc-sibling CPU #0 is not on the same node!

On Tue, Feb 26, 2013 at 9:49 PM, Yasuaki Ishimatsu
<isimatu.yasuaki@...fujitsu.com> wrote:
> 2013/02/27 14:11, Yinghai Lu wrote:
>>
>> On Tue, Feb 26, 2013 at 8:43 PM, Yasuaki Ishimatsu
>> <isimatu.yasuaki@...fujitsu.com> wrote:
>>>
>>> 2013/02/27 13:04, Yinghai Lu wrote:
>>>>
>>>>
>>>> On Tue, Feb 26, 2013 at 7:38 PM, Yasuaki Ishimatsu
>>>> <isimatu.yasuaki@...fujitsu.com> wrote:
>>>>>
>>>>>
>>>>> 2013/02/27 11:30, Yinghai Lu wrote:
>>>>>>
>>>>>>
>>>>>> Do you mean you can not boot one socket system with 1G ram ?
>>>>>> Assume socket 0 does not support hotplug, other 31 sockets support hot
>>>>>> plug.
>>>>>>
>>>>>> So we could boot system only with socket0, and later one by one hot
>>>>>> add other cpus.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> In this case, system can boot. But other cpus with bunch of ram hot
>>>>> plug may fails, since system does not have enough memory for cover
>>>>> hot added memory. When hot adding memory device, kernel object for the
>>>>> memory is allocated from 1G ram since hot added memory has not been
>>>>> enabled.
>>>>>
>>>>
>>>> yes, it may fail, if the one node memory need page table and vmemmap
>>>> is more than 1g ...
>>>>
>>>
>
>>>> for hot add memory we need to
>>>> 1. add another wrapper for init_memory_mapping, just like
>>>> init_mem_mapping() for booting path.
>>>> 2. we need make memblock more generic, so we can use it with hot add
>>>> memory during runtime.
>>>> 3. with that we can initialize page table for hot added node with ram.
>>>> a. initial page table for 2M near node top is from node0 ( that does
>>>> not support hot plug).
>>>> b. then will use 2M for memory below node top...
>>>> c. with that we will make sure page table stay on local node.
>>>>    alloc_low_pages need to be updated to support that.
>>>> 4. need to make sure vmemmap on local node too.
>>>
>>>
>>>
>>> I think so too. By this, memory hot plug becomes more useful.
>
>
> I agree with your idea. But I think above ideas is future work.
> So at first we should use movable memory for memory hot plug.
> After that, we will implement above ideas.
>
>
>>>
>>>>
>>>> so hot-remove node will work too later.
>>>>
>>>> In the long run, we should make booting path and hot adding more
>>>> similar and share at most code.
>>>> That will make code get more test coverage.
>>
>>
>> Tang,  Yasuaki, Andrew,
>>
>> Please check if you are ok with attached reverting patch.
>
>
> We will fix this problem with no objection. So please wait a while.
>
> And the problem occurs by "movablemem_map=srat" not
> "movablemem_map=nn[KMG]@ss[KMG]"
> At least, if you want to revert it, you should revert only
> "movablemem_map=srat" part.

Those patches are tangled together.

Also it looks funny to ask user to specify mem range in boot command
line to enable mem hotplug.

Thanks

Yinghai
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