Date: Mon, 5 Mar 2001 18:08:25 -0800 (PST) From: Matt Dillon <dillon@earth.backplane.com> To: Dan Phoenix <dphoenix@bravenet.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: systat -vmstat or iostat IO help Message-ID: <200103060208.f2628PT49635@earth.backplane.com> References: <Pine.BSO.4.21.0103051732370.6833-100000@gandalf.bravenet.com>
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:I am trying to figure out corelation between Inactive and Free then.
:Inact would be unused ram right?
:Free would be what how much of Active is being used? So what you are
:saying is if there is to much free then alot of active pages are being
:killed for some reason...as seen in error logs etc? ....just trying to get
:a quick overview of what a good accessment that was...never thought of
:that.
'free' (from systat -vm or top) is all that matters in your case.
Active/Inactive/Cache are best simply added together. Their
individual values will depend heavily on the load on the machine
because the VM system doesn't bother to keep things in their
proper queues if the memory load is low.
Normally when a machine is operating you see the 'free' value
drop steadily until it hits vm.v_free_min, which is typically
2-4 MB. The VM system then frees up inactive & cache memory
up to vm.v_free_target, which is typically around 10MB. Thus
the 'free' value will recover to around 10MB, then drop and
recover again, add nauseum.
Once free memory drops you should never see it get big again
unless you run a program which allocates a whole bunch of
memory (e.g. 40MB) and then exits. The allocated memory is
freed on program exit and may temporarily bump the 'free'
value up, but it should steadily drop again and restabilize
at 4-10MB or so. Alternatively it is possible that a whole
bunch of programs may be started at once and then all exit
at around the same time, resulting in the same effect.
If you regularly see a large free value (aka 40MB) plus lots
of disk activity, something weird may be going on that you
need to track down and figure out.
-Matt
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