From owner-freebsd-hackers  Wed Nov 20 18: 2:33 2002
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Date: Wed, 20 Nov 2002 18:02:30 -0800
From: David Schultz <dschultz@uclink.berkeley.edu>
To: Tony Finch <dot@dotat.at>
Cc: hackers@freebsd.org
Subject: Re: cvs commit: src/bin/sleep sleep.c
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Mail-Followup-To: Tony Finch <dot@dotat.at>, hackers@freebsd.org
References: <200211170158.gAH1wJhc035731@apollo.backplane.com> <20021117034219.13731.qmail@web41201.mail.yahoo.com> <20021117034219.13731.qmail@web41201.mail.yahoo.com> <E18EbhV-0008O5-00@chiark.greenend.org.uk>
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Thus spake Tony Finch <dot@dotat.at>:
> David Schultz <dschultz@uclink.Berkeley.EDU> wrote:
> >
> >BSS and modified data are not shared, and Matt is only counting
> >zero fill and COW faults.
> 
> Most of the BSS is mmapped zero pages that are copy-on-write, so in simple
> programs they should be mostly shared. See rtld-elf/map_object.c

Once those pages are written to, the kernel must fault in a fresh
zero-filled page.  Since the BSS typically holds uninitialized
data, we can probably assume that the program is going to
initialize most of it at some point, so there will be very few
shared BSS pages.

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