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Date:      Thu, 1 Aug 2002 11:09:40 -0400
From:      Rob Ellis <rob@web.ca>
To:        freebsd-questions@freebsd.org
Subject:   Re: 1GB ram, how much SWAP?
Message-ID:  <20020801150939.GF77297@web.ca>
In-Reply-To: <20020801042008.GD48188@wantadilla.lemis.com>
References:  <20020731171728.GH22253@web.ca> <87u1mfk9me.fsf@pooh.int> <20020731194842.GL22253@web.ca> <44ado7ejh7.fsf@be-well.ilk.org> <20020731211506.GN22253@web.ca> <20020801042008.GD48188@wantadilla.lemis.com>

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>o Even with light memory loads, the virtual memory system slowly pages out data
>  in preparation for a possible sudden demand for memory.  This means  that  it
>  can  be  more  responsive  to such requests.  As a result, you should have at
>  least as much swap as memory.

this is an argument for some swap, but i don't follow how it means
you need at least as much swap as memory... can you explain that a
bit more?

>o About the only ways to change the size of a swap partition are to add another
>  partition  or  to  reinstall  the system, so if you're not sure, a little bit
>  more won't do any harm, but too little can really be a problem.

if you find you're running out of swap, you can create swap files,
although i guess that's less efficient?

there's also the argument that if you ever plan to add more memory, you
want to add swap to prepare for that possibility. so one scenario
is that you want as much swap as the ram your machine can take +1MB.

in practice, though, if you add a lot of memory, you probably need less
swap (except for the kernel's preparation for swap it will never need ;-)
and for crash dumps). 

>  The  dump  routines can only dump to a single partition, so you need one that
>  is big enough.  If you have 512 MB of memory and two swap partitions  of  384
>  MB each, you still will not be able to dump.

is the average user going to be analyzing crash dumps? how often
does this come up? if dumpon is turned off by default, when would
you want to turn it on, what would you do after that...?

allocating 2GB+1M of swap on a new machine really isn't going to be 
a problem -- especially with cheap UDMA disks of 60GB+ -- but if it's 
just going to sit there, it offends my sense of economy... :-)

- rob

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