Clear the computer's memory?

[Alan McKinnon]

On Thursday 30 March 2006 09:47, Daniel Carrera wrote:
> Michael V. De Palatis wrote:
> > Yes, of course Firefox. Firefox is probably the WORST application
> > used on a day to day basis in terms of memory wastage. I've
> > stopped using it for that very reason.
>
> Yes. I don't understand how closing Firefox can give me back 200MB
> of RAM! That doesn't make sense at all. Firefox itself is what,
> 5MB? All I can guess is that it stores every page I visit in
> memory, which is stupid.

The binary does take up 5M, then it loads in all the plug-ins, and the 
extensions, then builds massive data structures in memory so it can 
parse the HTML, then still caches everything in sight. That's the 
default - there are settings in about:config to change this 
bahaviour. Mozilla released a statement recently about this, it 
should be on their web site.

<snip>

> You know what would be nice, if there was a tool that told me how
> much memory an application is using. Yes, I know about 'top', but
> after reading the man pages I can't figure out how to sort the
> processes according to how much memory they take. There used to be
> an application called 'gtop' (Gtk top) which was really good. I'm
> not usually into GUI stuff when the CLI will do, but this was a
> case where I thought the GUI was worth it.

top lies. ps also lies.

The reason is shared memory and libs. Firefox uses a bazillion libs 
and they add up to a gazillion bytes. But many other apps use the 
same libs so the output of top and ps is misleading.

When you shut down Firefox, it will go away and the kernel does a good 
job of reclaiming that memory. Not necessarily all at once either, 
but if it needs that 50M that isn't actually in use anymore, then it 
gets reclaimed. If you know Java, the parallels with the garbage 
collector are striking.

And, the kernel grabs most of the remaining RAM for disk buffers and 
caches just in case it needs them. These can be flushed and reclaimed 
quickly if an app needs memory.

Hence the oddity of a 1G machine sitting there doing nothing and 99% 
of memory apparently in use.

-- 
Alan McKinnon
alan at linuxholdings dot co dot za
+27 82, double three seven, one nine three five