Date: Mon, 26 Feb 1996 21:24:43 +0100 (MET) From: Luigi Rizzo <luigi@labinfo.iet.unipi.it> To: hackers@freebsd.org Subject: RAM compression again Message-ID: <199602262024.VAA01280@labinfo.iet.unipi.it>
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I have been thinking a little bit on the subject. I have come out with a relatively simple zero-removal algorithm which compresses (and decompressed) a 4KB page in about 100us (yes, that's 40MB/s) on a Pentium 100. While the compression ratio is not as high as with gzip, I consistently get a 2.5 reduction on FreeBSD 2.1R and 1.1.5 (maybe this is an artifact of the inefficient malloc) and on Alpha/OSF (64-bit architecture, known not to make a very efficient use of memory). More interesting is that some 15-20% of the pages compress to 64-bytes or less. Thus a very effective RAM-swap area could be implemented with little cost and additional complexity (with fixed-size, 64-bytes blocks). A description of the compression/decompression algorithm and its implementation are available from the following URL: http://www.iet.unipi.it/~luigi/research.html I'd be interested if someone could try it on a more recent system than 2.1R and report the results. Thanks Luigi ==================================================================== Luigi Rizzo Dip. di Ingegneria dell'Informazione email: luigi@iet.unipi.it Universita' di Pisa tel: +39-50-568533 via Diotisalvi 2, 56126 PISA (Italy) fax: +39-50-568522 http://www.iet.unipi.it/~luigi/ ====================================================================
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