Re: Need some help in understanding sparsemem.

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Fri, 9 Jul 2010 12:35:17 +0530
naren.mehra@gmail.com wrote:

> Thanks to you guys, I am now getting a grip on the sparsemem code.
> While going through the code, I came across several instances of the following:
> #ifndef CONFIG_NEED_MULTIPLE_NODES
> .
> <some code>
> .
> #endif
> 
> Now, it seems like this configuration option is used in case there are
> multiple nodes in a system.
> But its linked/depends on NUMA/discontigmem.
> 
> It could be possible that we have multiple nodes in a UMA system.
> How can sparsemem handle such cases ??
> 

sparsemem can be used both in UMA/NUMA case. IOW, sparsemem is for handling
memmap(array of struct page) for flexible memory layout, and not for NUMA.
Then, NUMA/MULTIPLENODE and SPARSEMEM has no relationship, basically.
"nid" is recorded just for detecting the nearest node for allocating mem_map.
(And some 32bit arch recoreds some information of 'nid'.)

So, you shouldn't be suffer from an illusion of sparsemem when you think about
NUMA/MULTIPLENODE. please visit free_area_init_nodes(), and add_active_range(),
remove_actitve_range(). They are for MULTIPLENODES.

Thanks,
-Kame

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