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From: "John S. Dyson" <toor@dyson.iquest.net>
Message-Id: <199803211658.LAA04264@dyson.iquest.net>
Subject: Re: No disk cache after memory upgrade (2.2/pii-300/512mb)
In-Reply-To: <199803210119.WAA21371@gaia.coppe.ufrj.br> from Joao Carlos Mendes Luis at "Mar 20, 98 10:19:14 pm"
To: jonny@coppe.ufrj.br (Joao Carlos Mendes Luis)
Date: Sat, 21 Mar 1998 11:58:28 -0500 (EST)
Cc: robh@imdb.com, stable@FreeBSD.ORG
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> #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.

John

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