Re: [PATCH 1/1] memhp: Add hot-added memory ranges to memblock before allocate node_data for a node.

[Tang Chen]

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@xxxxxxxxxx>
> > > 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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