Date: Fri, 4 May 2001 09:22:00 -0700 (PDT) From: Matt Dillon <dillon@earth.backplane.com> To: Doug Hardie <bc979@lafn.org> Cc: Mike Smith <msmith@FreeBSD.ORG>, Marius <marius@mail.communityconnect.com>, Ramon A Hermon <rahermon@iastate.edu>, freebsd-stable@FreeBSD.ORG Subject: Re: Mem Use Message-ID: <200105041622.f44GM0t25871@earth.backplane.com> References: <200105040206.f4426RJ05318@mass.dis.org> <f04330114b717c308aab4@[10.0.1.100]>
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:>> My systems look very much like this also. Do note that there is 87
:>> MB free and 1 MB that some time in the past got swapped out.
:>
:>That's 87MB of totally unused memory, ie. wasted money. 8)
:
:Exactly. And it also slows down other disk I/O. Why doesn't it swap
:it back in and leave it? It keeps bringing it back in every couple
:seconds. I don't see any swap out activity, only lots of swapin.
:...
:--
:-- Doug
If you are seeing swapin activity but no swapout activity it is
typically due to a program that is randomly accessing a large
memory address space slowly. 'named' is a really good example of
this. The program is accessing the address space slowly enough
that system pressures cause the system to reuse the memory at
around the same rate -- giving it to other processes that need it
more.
The system will always allocate free memory before anything else,
so if you have 87MB of free memory it's probably transient (that is,
you are doing other things in your system that eat up the memory
temporarily, then exit and free it all). Having free memory will not
prevent swapins from occuring, but if you do not have a transient
load that is causing large portions of memory to be freed then the
swapin activity *will* slowly use up the free memory.
swapin activity that is less then 100KB/sec will not have any appreciable
effect on disk performance. In general swapin activity of any kind
does not have nearly the effect that swapout activity has.
-Matt
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