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Re: [vox-tech] Three Install Questions
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Re: [vox-tech] Three Install Questions



On Fri, 18 Feb 2005, Wilson Shealy wrote:

> 1.  Are there any disadvantages (except disk space) to having an
> oversized Swap partition?  I've decided to double mine so that I can
> double my RAM at a future date.

I'm just gonna tackle question #1.

First off, most people don't think there's a problem having too much swap
partition, but I don't think anyone here really has hard data.  I don't
have hard data here either, so take everyone's remark with a grain of
sand.

Second, Rod is right -- you'll end up using more RAM for page tables.  In
this particular case, it's not going to impact your system that much since
you're only doubling your swap size.  So don't think it's okay to just
keep increasing swap partition size and not impact your system.  There's
some OS notion of paging the page tables but I'm not sure if Linux uses
it.

Third, as the size of the swap space increases, its usefulness drops.
The only way for you to utilize all the swap space is if you end up with a
really large program/data, or lots of small programs, or a combination of
both.  You wouldn't want to run lots of small programs together to fill up
your swap space since you'll either end up having to put most of them to
sleep, or each small program will constantly swap in-and-out and bring
down your system to a scratching halt.  A large program (or several large
programs) will probably utilize large swap space better since most of the
program will stay in swap space and only the portions you do use will load
up in memory.  But even in that case, you'll want all the used portions of
the program in RAM.

So let's look at the scenario where you have several large programs
running concurrently on your system.  To get the best performance out of
your computer configuration, you would want all the used portions of the
programs in RAM and the rest in swap.  Assuming that 30% of all the
running programs (or more accurately processes, shared libs, etc., except
for the kernel which you have to count 100% because it never gets swapped)
are actually used and the rest are not, you'd want your ideal swap
partition to be (100%-30%)/30% = ~3 times your RAM size.  Speaking really
broadly, any more than that and there will be some sluggishness or wasted
swap space; any less and you'll be running out of memory.  Of course, some
sluggishness is okay, but too much will definitely make the computer
unusable.

I'm just speaking broadly and those numbers are just made up.  I'm just
saying you DO have a reason to stop increasing your swap partition size at
some point -- just keep increasing won't give you a proportional return
for your investment because you'll either end up with a really slow
computer or wasted investment.  At some point, you'll want to actually
invest in RAM rather than your swap space.  For now, though, if you
haven't noticed any sluggishness with the previous setup then doubling
your swap partition probably won't do you any harm even if it doesn't do
you good.

-Mark


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Mark K. Kim
AIM: markus kimius
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