From owner-freebsd-stable  Sun Apr  5 18:47:46 1998
Return-Path: <owner-freebsd-stable@FreeBSD.ORG>
Received: (from majordom@localhost)
          by hub.freebsd.org (8.8.8/8.8.8) id SAA21889
          for freebsd-stable-outgoing; Sun, 5 Apr 1998 18:47:46 -0700 (PDT)
          (envelope-from owner-freebsd-stable@FreeBSD.ORG)
Received: from dyson.iquest.net (dyson.iquest.net [198.70.144.127])
          by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id SAA21642;
          Sun, 5 Apr 1998 18:46:21 -0700 (PDT)
          (envelope-from toor@dyson.iquest.net)
Received: (from root@localhost)
	by dyson.iquest.net (8.8.8/8.8.8) id UAA06954;
	Sun, 5 Apr 1998 20:46:01 -0500 (EST)
	(envelope-from toor)
From: "John S. Dyson" <toor@dyson.iquest.net>
Message-Id: <199804060146.UAA06954@dyson.iquest.net>
Subject: Re: swap-leak in 2.2.5 ?
In-Reply-To: <199804060140.SAA03046@ns.frihet.com> from "David E. Tweten" at "Apr 5, 98 06:40:39 pm"
To: tweten@frihet.com (David E. Tweten)
Date: Sun, 5 Apr 1998 20:46:01 -0500 (EST)
Cc: dswartz@druber.com, dyson@FreeBSD.ORG, dg@root.com, dag-erli@ifi.uio.no,
        stable@FreeBSD.ORG
X-Mailer: ELM [version 2.4ME+ PL38 (25)]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: owner-freebsd-stable@FreeBSD.ORG
Precedence: bulk

> 
> The 4.4 BSD interaction between physical pages used for virtual memory and 
> physical pages used for file system cache doesn't work that way, and I can't 
> imagine the FreeBSD core team adding in such a botch.  It is never a good 
> idea to send a dirty file system cache page to swap.  It is always better to 
> send it to the file system.  After all, it might never again be written.  If 
> it is ever written, it will have to be read into memory again either way.
>
Of course, we write dirty pages only to the correct place.

> 
> What you see in swap under heavy I/O load, is dirty process virtual memory 
> pages moved out of real memory to make way for an expanding file system 
> cache.  There's no reason to read them back until the process faults for 
> them; it might exit first, allowing you to just abandon them.
> 
Our filesystem cache applies only very slight pressure to process memory.
Indeed much less than most other OSes.

John


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-stable" in the body of the message