From owner-freebsd-hackers Wed Feb 17 10:39:16 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from smtp03.primenet.com (smtp03.primenet.com [206.165.6.133]) by hub.freebsd.org (Postfix) with ESMTP id C826811379 for ; Wed, 17 Feb 1999 10:39:13 -0800 (PST) (envelope-from tlambert@usr07.primenet.com) Received: (from daemon@localhost) by smtp03.primenet.com (8.8.8/8.8.8) id LAA03409; Wed, 17 Feb 1999 11:38:58 -0700 (MST) Received: from usr07.primenet.com(206.165.6.207) via SMTP by smtp03.primenet.com, id smtpd003290; Wed Feb 17 11:38:41 1999 Received: (from tlambert@localhost) by usr07.primenet.com (8.8.5/8.8.5) id LAA20158; Wed, 17 Feb 1999 11:38:39 -0700 (MST) From: Terry Lambert Message-Id: <199902171838.LAA20158@usr07.primenet.com> Subject: Re: vm_page_zero_fill To: dyson@iquest.net Date: Wed, 17 Feb 1999 18:38:39 +0000 (GMT) Cc: tlambert@primenet.com, toasty@home.dragondata.com, mike@smith.net.au, hackers@FreeBSD.ORG In-Reply-To: <199902170307.WAA27574@y.dyson.net> from "John S. Dyson" at Feb 16, 99 10:07:35 pm X-Mailer: ELM [version 2.4 PL25] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > > The thing that appalled me was what you said about BSS being zero'ed > > in the kernel space using zeroed pages instead of as a result of an > > explicit zeroing by the execution class loader. > > That is the way that it works. Explict zeroing is wasteful because > it cannot easily take advantage of background prezeroing... However, > recently prezeroed pages make for efficient usage of cache. The zero > queue (and all others) are designed to take advantage of recent cache > usage. This is robbing Peter to pay Paul; in a way. The base assumption that you are hiding is that you aren't constrained by memory bandwidth. This isn't true if you are nearly saturating a PCI bus with 4 BT848's (to pick the highest memory bandwidth application I know about). Maybe we need to go back to first principles, and examine the assumptions about what constraints are in effect under various usage models, and make trades like these optional instead of mandatory. I think that's all he wants, anyway. In any case, it's always interesting when someone uses code in an unexpected way. 8-). Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message