Date: Wed, 4 Mar 1998 03:26:54 -0500 (EST) From: "John S. Dyson" <dyson@FreeBSD.ORG> To: dwhite@resnet.uoregon.edu Cc: mike@chaski.com, questions@FreeBSD.ORG Subject: Re: page faults etc. Message-ID: <199803040826.DAA00336@dyson.iquest.net> In-Reply-To: <Pine.BSF.3.96.980303200746.21429K-100000@gdi.uoregon.edu> from Doug White at "Mar 3, 98 08:09:04 pm"
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Doug White said: > On Tue, 3 Mar 1998, michael dorin wrote: > > > > > How do I tell how many page faults my system is having? > > systat -vmstat <delay>, Trp item (this is total system traps, but includes > page faults). > Page faults are generally not useful info. That info is more useful to me to make sure that I have minimized them. There are sort-of three levels of faults, one that requires I/O to complete, one that requires copying or zeroing a page, and one that simply maps a page into memory. These are listed in descending time to process, and the times span several orders of magnitude or more. > > > What do I look for as bad? > > What do I look for as good? > > You really want to be concerned about swap usage, this is probably an > easier-to-track barometer. If your swap system is very active (lots of > in/out) you probably need more RAM. > > Mr. Dyson? > Yes, the paging I/O is the most important parameter, and too much I/O will impact performance severely. FreeBSD tries to minimize the amount of paging I/O by careful page mgmt, but excessive paging will clobber performance on any system. One more note though, if you have excess RAM, the system will likely use it as a very effective disk cache. There is a point of diminishing returns. With my workstation workload, it seems that I am at that point between 64MB and 128MB. Performance is still reasonable at 32MB with my workload. When running on 16-32MB, the system starts feeling like WinNT with 64MB. I normally run with 200+ MB, but with memory so cheap, why not? :-). -- John | Never try to teach a pig to sing, dyson@freebsd.org | it just makes you look stupid, jdyson@nc.com | and it irritates the pig. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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