swap on FC1

Tom 'Needs A Hat' Mitchell mitch48 at sbcglobal.net
Mon Apr 12 19:37:16 UTC 2004

On Mon, Apr 12, 2004 at 08:50:33PM +0200, Pierre De Boeck wrote:
> I have FC1 on my Dell inspiron 5150 and I use System Monitor
> to control the memory used.
> I have 512MB of RAM and 1GB of swap file. What I observed when
> I have not started any application (except some deamons) is that
> 1) the "used memory" is 370 of 502
> 2) the used swap is 0 of 1020
> And when I launch 2 or 3 apps like emacs or mozilla the
> used swap is ALWAYS 0 of 1020.
> Is it normal? Will the swap be only used when the used 
> memory will reach the full capacity available?

In general Linux will only use swap when it needs to.

It will however use memory as cache for any page of program text or
file information it happens to have looked at.

Large processes like emacs will cause lots of pages to be read into memory.
So the first time you start emacs it will seem slow then a second time
startup can be very quick.

When a process like emacs exits the pages it used will stay cached
unless needed by some other task.   

The net result is that all of memory will appear to be used much of
the time.

When a process starts up and needs memory the OS can inspect it's
cached pages find one that is not in use,  toss the cached
information, clean the page and give it to the process.

	T o m  M i t c h e l l 
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