Date: Sat, 10 Feb 1996 05:55:17 -0500 (EST) From: Peter Dufault <dufault@hda.com> To: luigi@labinfo.iet.unipi.it (Luigi Rizzo) Cc: hackers@FreeBSD.ORG Subject: Re: Compressed RAM/SWAP Message-ID: <199602101055.FAA09574@hda.com> In-Reply-To: <199602101043.LAA04471@labinfo.iet.unipi.it> from "Luigi Rizzo" at Feb 10, 96 11:43:51 am
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> > > If there are lots of zero'd pages that aren't used that often, > > can't be eliminated, and would benefit from compression wouldn't > > it be better to look at a ZFOD (zero fill on demand) mechanism? > > But this only works if the pages are not accessed at all. The first > time they are accessed they must be filled up. Well, yes, but for reads they can all point to the same underlying page, and for writes you're changing them anyway (and if you are sure the writes have to happen before they are accessed again you don't even need to fill them). If the problems are lots of zero pages it seems that there is a better way than compression, though I guess you can argue this is just compression optimized for zero pages. I better back off this discussion as it is outside my usual work. I'll let someone who knows this stuff comment. -- Peter Dufault Real-Time Machine Control and Simulation HD Associates, Inc. Voice: 508 433 6936 dufault@hda.com Fax: 508 433 5267
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