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Date:      Wed, 26 Jun 2002 02:46:25 -0700
From:      Terry Lambert <tlambert2@mindspring.com>
To:        Matthew Dillon <dillon@apollo.backplane.com>
Cc:        Peter Wemm <peter@wemm.org>, Alfred Perlstein <bright@mu.org>, Patrick Thomas <root@utility.clubscholarship.com>, freebsd-hackers@FreeBSD.ORG
Subject:   Re: tunings for many httpds...
Message-ID:  <3D198D71.86779927@mindspring.com>
References:  <20020625222632.B7C7D3811@overcee.wemm.org> <3D1970E7.697D4A49@mindspring.com> <200206260758.g5Q7wPgZ019100@apollo.backplane.com>

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Matthew Dillon wrote:
>     Hmm.  I'm fairly sure that Linux does not quite do it that way.  I
>     believe the 2-level page tables are copy-on-write, but that only
>     gives you shareability across a fork() and then only for a little
>     while.  I'm fairly certain that Linux cannot share page tables
>     for post-fork modifications (like when you mmap() or get a SysV
>     shared segment).  The rmap patches are roughly equivalent to our
>     i386 pmap code and allow Rik to implement page queues and proper page
>     aging.

I wasn't saying that they were shared on the mmap(); Peter had
suggested it for FreeBSD.

Also "a little while" is relative; as long as you don't write
the page, it should stay shared.  That basically means that all
instances of apache share mappings on the code pages.

Here's the article I was reading in one window while typing in the
other.  It's linked off the article reference I posted to -arch
earlier:

	http://old.lwn.net/2002/0124/kernel.php3
	"What Rik van Riel is up to."

FWIW: In the original Article:

	http://lwn.net/Articles/3327/

they say they've gon to a 3 level page table scheme for the Hammer
port.

-- Terry

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