Date: Wed, 17 Feb 1999 18:38:39 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: dyson@iquest.net Cc: tlambert@primenet.com, toasty@home.dragondata.com, mike@smith.net.au, hackers@FreeBSD.ORG Subject: Re: vm_page_zero_fill Message-ID: <199902171838.LAA20158@usr07.primenet.com> In-Reply-To: <199902170307.WAA27574@y.dyson.net> from "John S. Dyson" at Feb 16, 99 10:07:35 pm
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> > 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
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