[MUD-Dev] Re: TECH: Distributed Muds

Matthew D. Fuller fullermd at over-yonder.net
Sun Apr 29 22:34:46 New Zealand Standard Time 2001


On Fri, Apr 27, 2001 at 12:49:35PM -0400 I heard the voice of
Derek Snider, and lo! it spake thus:

> Depends on the Unix system.  BSD requires double the VM as RAM.
> That is a terrible waste of disk space.  With Linux you can get away
> with using little or no VM.

BSD requires no such thing.  Most BSD manuals will tell you to
configure at least double the swap as you have physical RAM, because
for a very very long time, that was conventional wisdom for a starting
figure, and it's still (IMO) a reasonable beginning approximation.  Of
course, it requires tuning based on your given workload.  You also
want one swap partition bigger than your physical RAM if you want to
be able to take system crashdumps.  And finally, at least in the case
of FreeBSD, the VM system is more agressive than the norm at paging
out unused pages and maintaining a larger in-core free memory pool.

None of this, however, translates to "needs more swap".  And get your
terminology straight; ever *nix system on the market has at least as
much 'VM' as RAM, since everything happens in VM; the VM sections are
just mapped to physical RAM, or swap space, or nothing, etc, as
appropriate.  I'm fairly sure that most *nix systems will allow you to
disable paging (or even discourage it, which is even better) while
still leaving swapping enabled.  However, I can't see how that is very
often desirable.  If your I/O subsystem is slow enough that this is
causing a problem, and you have little enough RAM relative to your
data set that the problem is common, you have much bigger problems.


--
Matthew Fuller     (MF4839)     |    fullermd at over-yonder.net
Unix Systems Administrator      |    fullermd at futuresouth.com
Specializing in FreeBSD         |    http://www.over-yonder.net/
       "Klein bottle for sale ... inquire within."
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