On Fri, 11 Jul 2008 11:10:28 -0400, Mary Anne Matyaz
<[EMAIL PROTECTED]> wrote:

>Question on paging though. You're supposed to have, like twice the amoun
t of
>allocated guest memory in paging space. So assuming I do, will I ever fi
ll
>it up?
>IE, if I total up the memory from user direct, double it, and have that 
much
>paging
>space (though I have tripled it to be safe), can I ever fill it up?
>
>Thanks,
>Mary Anne
>

Yes, if everyone really followed that guideline properly all of the time,

then paging would (or at least should) never fill up and overflow to spoo
l,
and this concern would be moot.  Unfortunately, it does happen, for lots 
of
different reasons, as Rob points out.  

Also, you really want the total virtual storage load, not just guest memo
ry,
so for example, you'd want to also include the maximum amount of vdisk sp
ace
allowed.  (Likely covered by your tripling, though.)  

As for why it's twice rather than just a simple "greater than", that's to

avoid excessive fragmentation of paging space to allow for decent amounts
 of
contiguous available paging space and good blocking.  

- Bill Holder
  z/VM Development, IBM

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