linux-kernel - Re: [PATCH 1/1] memhp: Add hot-added memory ranges to memblock before allocate node

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Date:	Wed, 26 Aug 2015 14:45:50 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Xishi Qiu <qiuxishi@...wei.com>
CC:	<akpm@...ux-foundation.org>, <isimatu.yasuaki@...fujitsu.com>,
	<n-horiguchi@...jp.nec.com>, <vbabka@...e.cz>,
	<mgorman@...hsingularity.net>, <rientjes@...gle.com>,
	<kamezawa.hiroyu@...fujitsu.com>, <izumi.taku@...fujitsu.com>,
	<yasu.isimatu@...il.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>
Subject: Re: [PATCH 1/1] memhp: Add hot-added memory ranges to memblock before
 allocate node_data for a node.


On 08/25/2015 09:09 AM, Xishi Qiu wrote:
> On 2015/8/24 17:22, Xishi Qiu wrote:
>
>> On 2015/8/24 1:06, Tang Chen wrote:
>>
>>> The commit below adds hot-added memory range to memblock, after
>>> creating pgdat for new node.
>>>
>>> commit f9126ab9241f66562debf69c2c9d8fee32ddcc53
>>> Author: Xishi Qiu <qiuxishi@...wei.com>
>>> Date:   Fri Aug 14 15:35:16 2015 -0700
>>>
>>>      memory-hotplug: fix wrong edge when hot add a new node
>>>
>>> But there is a problem:
>>>
>>> add_memory()
>>> |--> hotadd_new_pgdat()
>>>       |--> free_area_init_node()
>>>            |--> get_pfn_range_for_nid()
>>>                 |--> find start_pfn and end_pfn in memblock
>>> |--> ......
>>> |--> memblock_add_node(start, size, nid)    --------    Here, just too late.
>>>
>>> get_pfn_range_for_nid() will find that start_pfn and end_pfn are both 0.
>>> As a result, when adding memory, dmesg will give the following wrong message.
>>>
> Hi Tang,
>
> Another question, if we add cpu first, there will be print error too.
>
> cpu_up()
> 	try_online_node()
> 		hotadd_new_pgdat()
>
> So how about just skip the print if the size is empty or just print
> "node xx is empty now, will update when online memory"?

As Liu Jiang said, memory-less node is not supported on x86 now.
And he is working on it.

Please refer to https://lkml.org/lkml/2015/8/16/130.

About your question, now, node could only be onlined when it has some 
memory.
So the printed message is also about memory, and sis put in 
hotadd_new_pgdat() .
I think the author of the code didn't think about online a node when a 
CPU is up.

But now, memory-less will be supported. So, I think, as you said, the 
message should
be modified.

But how it will go, I think we should refer to Liu Jiang's patch, and 
make a decision.

Thanks.

>
> Thanks,
> Xishi Qiu
>
>>> [ 2007.577000] Initmem setup node 5 [mem 0x0000000000000000-0xffffffffffffffff]
>>> [ 2007.584000] On node 5 totalpages: 0
>>> [ 2007.585000] Built 5 zonelists in Node order, mobility grouping on.  Total pages: 32588823
>>> [ 2007.594000] Policy zone: Normal
>>> [ 2007.598000] init_memory_mapping: [mem 0x60000000000-0x607ffffffff]
>>>
>
>
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