OS X “Swap used”

Question

I'm a bit confused here, I'm trying to open a tab in Chrome and sometimes it takes few seconds while freezing my computer significantly so that I can't use even to bring Dock menu...

I even closed ALL of my applications at one point and Activity Monitor still reads that my "Swap used" 2G, while showing me my Free: is 1.1G, while everything is closed other then Activity Monitor.

from what I understand generally whenever swap is used that means it's start using my HDD as additional memory and uses I/O from HDD and since HDD is slower then RAM it slows down my computer.

now I have 4GB RAM in my MacBook Pro, so I shouldn't having any issues keeping open few applications, I don't really use all that much yet somehow I run into this issue quite often, I'd say on pretty much daily basis...

What can I do in order to check what's uses most of my memory? or better yet what's being used by SWAP?!

Answer 1

This isn't a complete answer to your question, but be aware that VM is sometimes used for memory mapped file I/O. That's where an process tells the VM system to map a file that's currently on disk into a part of the process's virtual address space. That is, treat the disk blocks where a certain file resides as swapped-to-disk VM pages, so the app can easily get arbitrary blocks of the file loaded into RAM quickly just by reading those addresses in memory. So even when you have so much RAM you should never need swap, sometimes processes use VM swapping as a convenient way to load parts of files.

I have no idea if that's what Chrome is doing in your particular example, which is why I say this isn't a complete answer, but it's something to be aware of. It's not uncommon to have VM in use even while there's still free RAM.