Re: question about memory-hotplug

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

> In the traditional linux without sparsemem, there are node-zone-memmap 
> mechanism for managing the physical memory,is it right?

Yes.

> while in the sparsemem mechanism, what is the architure of 
> node-zone-memmap or node-zone-mem_section[]-mem_map like?

mem_section[] is "static array" which is defined in sparse.c.
So, no pointer is necessary to point mem_section array.
Its index can be found by only pfn like ((pfn >> PFN_SECTION_SHIFT)).
Each mem_section has pointer of mem_map.

In addition, each page->flags has area for saving mem_section's index.
page_to_section() is (page->flags >> SECTIONS_PGSHIFT) & SECTIONS_MASK).

Tracing __pfn_to_page() and __page_to_pfn in 
include/asm-generic/memory_model.h will be good answer 
for your understanding.

> and if the sparsemem is on , buddy still does its work in a mem_map as 
> before or does it work in a new way?

2.6.10 or older kernel has bitmaps to manage buddy page. Current
one doesn't have it. Its information is saved in page->private.
Others are same.
1 section size is bigger than MAX_ORDER. So, current buddy system
doensn't concern about section size. 
This means memory hotplug unit size is section size. (At least now)

> and how does virt-to-phy macro (or something like it) work,when there 
> are a list of mem_map in the sparsemem system?
> 
> > (However, x86-64 code has original code. IIRC, its memmap was allcated 
> >  statically....)
> >   
> does x86-64 not surpport the memory-hotplug,or how does it achieve the 
> memory-hotplug ?

x86-64 supports both of sparse and non sparse. It is seleced by
kernel config option.

Bye.

-- 
Yasunori Goto 



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