Re: question about memory-hotplug

[Yasunori Goto <y-goto@jp.fujitsu.com>]

Hello.

> hi
>   I try to understand the memory_hotplug.c   ,but I am confused about 
> the mechanism in it
>  Does the mem_map is allocated when setup for all the memory page both 
> the existing and the hotplug , or  does the mem_map is allocated 
> dynamically when a chip of memory is hotpluged ?
>  if mem_map is allocated dynamically,does the mem_map is maintained in 
> the list or how to deal with it ?
>  and if mem_map is allocated dynamically,does system need new node and 
> new zone structure to manage the dynamically-allocated memmap ,or not ?

Basically, memory hotplug code depends on sparsemem. So, I'll
recommend that you should see mm/sparse.c too.
In sparsemem code, mem_map is allocated dynamically, and 
its pointed by mem_section[] array.

(However, x86-64 code has original code. IIRC, its memmap was allcated 
 statically....)

>  if  system need new node and new zone structure to manage the 
> dynamically-allocated memmap,does system have to be a NUMA-surpport one 
> or not?

Pgdat and zone can be allocated dynamically for NUMA system,
but memmap is not pointed by them if sparsemem is on.

Thanks for your concern. :-)

---
Yasunori Goto 



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