Date: Mon, 19 Apr 1999 15:38:59 -0500 (EST) From: "John S. Dyson" <dyson@dyson.iquest.net> To: dillon@apollo.backplane.com (Matthew Dillon) Cc: dg@root.com, hackers@freebsd.org Subject: Re: Directories not VMIO cached at all! Message-ID: <199904192039.PAA20464@dyson.iquest.net> In-Reply-To: <199904182002.NAA81858@apollo.backplane.com> from Matthew Dillon at "Apr 18, 99 01:02:47 pm"
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> > I see an advantage both ways. Not only are we able to use the VM cache > to cache directories ( and thus scale directory operations to memory ), > but I don't think there is even a downside to mapping whole pages even for > small directories. The reason is simple: When you access small > directories you tend to access specific files in said directories. When > you access specific files, there's a good chance they will be in the namei > cache. If they are in the namei cache, the VMIO mapping will not be > referenced very often for most small directories which means that the > VM cache will throw it away. Hence, no waste. > I cannot believe that you said that: The size of the cache buffers are then up to 8X larger when using a whole page instead of a 512byte buffer. BTW, VMIO is a misnomer, and I named it... VMIO was an earlier incarnation, and some of it spilled into the existant code. Again, do a study to find out if the internal fragmentation makes things worse. Don't depend on the VM code to just "throw" things away -- if you can make considered decisions instead of deferring them to a policy somewhere, make the decision... John To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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