Date: Sun, 26 Jul 1998 21:53:27 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: green@zone.baldcom.net (Brian Feldman) Cc: freebsd-current@FreeBSD.ORG Subject: Re: New LINT options: what is VM coloring? Message-ID: <199807262153.OAA17869@usr01.primenet.com> In-Reply-To: <Pine.BSF.4.00.9807251808530.6651-100000@zone.baldcom.net> from "Brian Feldman" at Jul 25, 98 06:11:47 pm
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> Would anyone mind letting me in on exactly what "VM coloring" is, and > especially whether or not I should define one of these?: > # Options for the VM subsystem > #options PQ_NOOPT # No coloring > options PQ_LARGECACHE # color for 512k/16k cache > #options PQ_HUGECACHE # color for 1024k/16k cache > As far as I can tell, it would seem these would be options to set certain > parameters to optimal as far as the VM subsystem goes, and if so, is it > safe to use one? ] Page Coloring uses the operating system to control the mapping of ] virtual to physical address by controlling the physical memory page ] which virtual pages are allocated to. Coloring becomes useful when ] the page number is involved in cache indexing, i.e., for large, low ] associativity, first level caches: exactly the trends the industry ] is following. [ ... ] ] For these large physically-indexed caches, the use of the low-order ] bits of the physical page number (the color) in cache indexing ] involve the virtual to physical translation in the location of data ] in the cache. While the virtual address space is laid out very ] uniformly, the lack of control over the virtual-to-physical mapping ] by most operating systems causes the physical color (and therefore ] cache placement modulo the page size) to be ``randomly'' selected. ] Thus, depending on the order in which the physical pages are ] assigned, cache miss rate can vary significantly. See: http://umunhum.stanford.edu/res_html/great92/node13.html#SECTION00031000000000000000 Or click in William L. Lynch's name at: http://umunhum.stanford.edu/res_html/great92/node12.html For the full text of the paper. See also: http://www.pdl.cs.cmu.edu/SDI/todd_mowry.html (abstract) http://www-flash.stanford.edu/~bugnion/CDPC/ (full paper) 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-current" in the body of the message
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