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Re: Swap size recommendations



Luke S Crawford <lsc%prgmr.com@localhost> writes:

> John Hayward <John.C.Hayward%wheaton.edu@localhost> writes:
>
>> The NetBSD site recommends swap size be greater than 32Mb or memory
>> size as a base.

Swap size recommendations have been historically difficult.  The real
issue is that the person making the recommendation can't know what you
are going to do with the system.

Enduring points from the arguments:

  swap should be bigger than RAM, so you can have crashdumps

  RAM + swap should be big enough for the total virtual size of all the
  program s you want to run at once

  if programs are paging all the time, you should get more RAM somehow

Given all that, "make swap a little bigger than RAM" ends up being
pretty reasonable, because if that's not enough swap you really want
more RAM.

Then there are the less-widely-accepted arguments

  There are some programs that have a large VSZ but fairly small RSS.
  These use swap without actually using it much, and that's ok, so
  having bigger swap may make senes.

  If disk is cheap, you might as well have more swap than you need,
  because that won't hurt and it's very annoying to have not enough.

> well, the dom0 can't swap out guest memory, so you really will only
> be swapping out the dom0 memory, not the guest memory.   

true

> That said, I always give my Dom0s a little bit extra swap, just to give
> myself a little extra wiggle room if something does start using 
> unreasonable amounts of ram.

Me too.

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