Date: Wed, 02 Jun 1999 11:16:32 -0700 From: Jason Thorpe <thorpej@nas.nasa.gov> To: Arun Sharma <adsharma@home.com> Cc: hackers@FreeBSD.ORG Subject: Re: pv_table/pv_entry Message-ID: <199906021816.LAA14736@lestat.nas.nasa.gov>
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On Tue, 1 Jun 1999 18:08:35 -0700
Arun Sharma <adsharma@home.com> wrote:
> Going through the 4.4 BSD book, I learnt that the purpose of the pv_table
> is to be able to locate all the mappings to a given physical page.
>
> However, comparing this to the Linux approach, which chains vm_area_struct
> (analogous to vm_map_entry in FreeBSD) together to locate the shared
> mappings, it appears to me that the Linux approach is more space efficient.
>
> So why not eliminate pv_table and chain vm_map_entries together to represent
> the sharing information ?
....because in the Mach VM system (which is what FreeBSD is derived from),
map entries may represent several virtual (and thus physical) pages.
NetBSD's UVM is the same way.
-- Jason R. Thorpe <thorpej@nas.nasa.gov>
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