Questions about memory zone

Questions about memory zone

[ruby young]

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Hi, all~
I'm interested in memory of xen. And I wondered what does the real mean of
xen 'zone'. It seems different from linux 'zone'.
In the source code of xen-3.3.0/xen/common/page_alloc.c, there is defined:
#define pfn_dom_zone_type(_pfn) (fls(_pfn)-1)

and NR_ZONES is defined:
#define NR_ZONES (PADDR_BITS - PAGE_SHIFT)

It seems Zone in xen set up as physic address and are separate by the last
pfn bit set.
But Why does Xen Zone organize like this? And What does the Zone mean?

Best Wishes!


Ruby Young

-- 
Best wishes

杨漾
北京航空航天大学计算机学院体系结构研究所
电话:010-82338059-132
邮件:9907yruby@gmail.com
地址：北京市海淀区学院路37号北京航空航天大学新主楼 G座1026
--------------------------------------------------------------------------------
Yang Yang
Institute of Computer Architecture and System
BeiHang University（BUAA）
Tel: (86-10)82338059-132
Email: 9907yruby@gmail.com
Addr: Room 1026,Building G,The New Main Building,37# Xueyuan Rd.,Haidian
District, Beijing 100083, PRC

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Re: Questions about memory zone

[Jan Beulich]

>>> ruby young <yangyang@les.buaa.edu.cn> 05.05.09 10:05 >>>
>Hi, all~
>I'm interested in memory of xen. And I wondered what does the real mean of
>xen 'zone'. It seems different from linux 'zone'.
>In the source code of xen-3.3.0/xen/common/page_alloc.c, there is defined:
>#define pfn_dom_zone_type(_pfn) (fls(_pfn)-1)
>
>and NR_ZONES is defined:
>#define NR_ZONES (PADDR_BITS - PAGE_SHIFT)
>
>It seems Zone in xen set up as physic address and are separate by the last
>pfn bit set.

Correct.

>But Why does Xen Zone organize like this? And What does the Zone mean?

In order to be able to allocate memory based on address width restrictions,
without adding overhead on sorting memory as it gets (or after it got) freed.

Jan