[nflug] AMD64 Debian 'Etch' Stability

[Ken Smith]

On Wed, 2008-06-11 at 07:21 -0400, Cyber Source wrote:
> I was wondering if the swap usage 
> is related to the swap size in general, not necessarily the ram size.

No, swap is used only when something needs to be paged out of physical
memory (and that thing can't be paged back in from some other file on
the system - executable machine code for example won't be put into swap
because it can be reloaded from the executable file).  How much swap
space you have allocated won't play any factor in if/when that occurs at
all.

As you would know but mentioning for the sake of others, obviously the
more ram you have the less likely you will be of reaching the point
you're forced to start paging stuff out.  So in that sense swap usage is
related to ram size but that's the only sense they're related at all,
and how much swap space you have allocated won't play a factor in
that.  

There are only two things that will be effected by the amount of swap
space you allocate.  The first is the obvious one I'm sure you know but
I'm not quite sure if you know the second because I've run into some
quite advanced sys-admins who hadn't realized this one (depends heavily
on your specific experience).  If the machine crashes it can be told to
create a crash dump which in turn can be used by a kernel programmer to
try and debug why it crashed.  A crash dump is done by copying the
entire contents of physical memory into the swap space as the machine is
going down, and then copying it out of swap space into files (those
files usually in /var/crash) during the reboot.  So if you don't have as
much swap space as you have physical memory the machine can't do a crash
dump.

And again sorry about the previous message.  Next time I'll try to stick
strictly to answering your question and not wander off into a
description of stuff I think you might already know but others on the
list might not. [ That's not intended as a flame either, but it might
have contributed to what annoyed you along with the admittedly flippant
comment I'd made about being a young sys-admin.  I have a bad habit of
"talking to the list" instead of "talking to the originator" when
replying sometimes. ]

-- 
                                                Ken Smith
- From there to here, from here to      |       kensmith at cse.buffalo.edu
  there, funny things are everywhere.   |
                      - Theodore Geisel |