Date: Sat, 21 Mar 1998 18:56:26 +0000 (GMT) From: Rob Hartill <robh@imdb.com> To: stable@FreeBSD.ORG Subject: Re: No disk cache after memory upgrade (2.2/pii-300/512mb) Message-ID: <Pine.BSF.3.96.980321184632.8645B-100000@localhost> In-Reply-To: <199803211658.LAA04264@dyson.iquest.net>
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On Sat, 21 Mar 1998, John S. Dyson wrote: > > #define quoting(Rob Hartill) > > // > Yep... I get the same thing... one of our machines just sits there, always > > // > with free memory. It's never doing anything (it's rare to see any load at > > // > all) - the same with the others - but their cache fills up and they never > > // > have free memory. > > // > > > // > Bizare eh? > > // > > // Strangely, after about 24 hours of being cache-less, it suddenly came > > // to life again. I'm wondering if it's just not reporting the cache for > > // some unknown reason. > > > > Pay attention to the Active Memory size, and see if it grows with > > disk access. Disk cache can also be listed as Active Memory. > > I don't know exactly why, but this is most commom if your partitions > > are mounted async. > > > That is true. Note that all of your memory is used as a disk cache, if it > isn't used as program memory. The memory usage is less than your total > available memory only when the system is just started, or a program has > exited (or freed memory), a disk file has been deleted, or a filesystem > is dismounted. > > It is hard to tell if you need more memory, but maybe the best measure is > excessive swap pager activity. In our case, there was no swapping and we'd just doubled the physical memory 256->512 and with 256 it never (well rarely) swapped. With 256 we could see a cache of 30-50mb build up in a matter of minutes. Whatever it was, for now it's gone away and things are back to normal. You might scratch your head and ask why double the ram if you're not even close to swapping, well runing a mod_perl based Apache, having oodles of disk cache reduces the response times of our servers by 300-700%.. and the faster a httpd process can respond, the fewer of them you need to have running.. and the fewer you have running, the more free memory you have to give to the cache. -- Rob Hartill Internet Movie Database (Ltd) http://www.moviedatabase.com/ .. a site for sore eyes. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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