Virtual memory on Linux doesn't add up?

Question

I was looking at System Monitor on Linux and noticed that Firefox is using 441 MB of memory, and several other applications are using 274, 257, 232, etc (adding up to over 3 GB of virtual memory). So I switch over to the Resources tab, and it says I'm using 462 MB of memory and not touching swap. I'm confused. What does the virtual memory amount mean then if the programs aren't actually using it. I was thinking maybe memory they've requested but aren't using, but how would the OS know that? I can't think of any "I might need this much memory in the future" function..

Answer 1

First off, shared memory is not really (?) counted correctly by top. Second, yes, a program asks for rights to memory, and then uses it, but it may never touch any, and the OS knows that. No problem at all for every app to have allocated all the ram and swap, as long as they don't try to use it :-D > We are not in a Mac OS Classic world (in fact, that is how the old Ram Doubler worked, letting you use the difference between allocated and used).

Answer 2

Have you ever tried to fire "vmstat"?? iff not help yourself and fire it from the command line like this :

vmstat

And please RTFM for lessen your owes. I have seen couple of interesting flags there in the man page...which might help you to understand.Plus iff you are really concerned about firefox memory consumption.. then have at look at this solution..here

http://unixbhaskar.blogspot.com/2009/10/firefox-saga-on-opensuse.html

and here

http://unixbhaskar.blogspot.com/2010/02/cleanup-firefox-clogging-by-pruning-its.html

And iff you really interested know the Linux internals for dynamic memory allocation read here

http://www.ibm.com/developerworks/linux/library/l-linux-slab-allocator/index.html

And use one binary called " pmap"..use it like this pmap (process-id) to get to know how that particular application using memory inside.To know more about "man pmap".

I hope I have given you much insight get on.

Cheers!