Re: Swap partitions
Re: Swap partitions
- Subject: Re: Swap partitions
- From: Shawn Erickson <email@hidden>
- Date: Tue, 24 Feb 2004 13:42:35 -0800
On Feb 24, 2004, at 11:25 AM, Mickey S. wrote:
Hello,
I am new to the Darwin / MacOS world and I am looking for some
guidance. For starters I have heard any number of pros and cons about
the swap file system used in Darwin. I understand the basics of the
Dynamic Pager system ,but I am wondering why there appears to be a lack
if support to dedicated swap partitions. Is this a limitation of XNU?
or is this to make Apple's end users happy I.E. when they buy a 150G
disk they don't see 149G available. ;) .
It is not a limitation of XNU, if fact no limitation exists, one can
create swap partitions and target the pager at it. Of course doing so
is not a normal configuration or support by Apple (at least I don't
think Apple supports it).
If you want to do it do it... for more information on the dynamic page
try "man dynamic_pager". Just understand that is not normal and later
updates make break your redirected swap.
Having a swap partition will likely greatly limit how big the swap
file(s) can grow and hence limit what the system can do before running
out of virtual memory backing (which often leads to crashes...). So
slicing off a percentage of the relatively huge disks one gets in
systems today can be counter productive.
Some folks will state that having a swap partition reduces the chance
of file / swap file fragmentation. It does but the data in the swap
files is already greatly fragmented (for various obvious reasons) as is
the page in/out pattern and that is likely to be more of an issue then
fragmentation of swap file itself. Additionally if file fragmentation
of the swap is some how an issue, your system is already greatly
hindered by the swapping taking place, it will be the least of your
issues.
Now targeting an independent device for swap can make sense for some
folks / environments.
-Shawn
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