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Re: [Xen-devel] Questions about memory zone

from [Jan Beulich]

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To:	"ruby young" <yangyang@xxxxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] Questions about memory zone
From:	"Jan Beulich" <jbeulich@xxxxxxxxxx>
Date:	Tue, 05 May 2009 09:25:32 +0100
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>>> ruby young <yangyang@xxxxxxxxxxxxxxx> 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


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