[oclug] swap/memory tools
wisq-oclug at wisq.net
Mon Nov 29 09:53:14 EST 2004
On Mon, Nov 29, 2004 at 05:15:23AM -0500, GR Gaudreau wrote:
> I have 512 MB of RAM, do I really need a swap file?
Well, particularly if the space is already allocated, it shouldn't
hurt to activate it and let the kernel decide.
> Would I be better off with a cache... if I don't already have one?
> How do I know I have one, if I do?
You know you have one because you're running Linux. :) It's standard
in all the OSes these days, and DOS was pretty much the only OS I know
of where it a) wasn't available for many versions and b) was disabled
To see it 'in action', check out the output of 'free'. On my laptop
now after a night of inactivity:
total used free shared buffers cached
Mem: 508528 467556 40972 0 156280 59276
-/+ buffers/cache: 252000 256528
Swap: 979924 0 979924
Note the 'cached' field. This is the amount of physical RAM being
used to cache disk access. 'buffers' is kernel buffering.
Also note the '-/+' row; this is how much is actually being used by
programs, because the rest is being used for buffers and cache.
Another way to demonstrate this is to read a large file, then read it
again immediately. The second one should take much less time and
almost no disk access; that's because it came from the cache.
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