MacOS – Should I disable Virtual Memory on SSD in OS X Yosemite

I was doing some reading about inactive memory after wondering about it myself. My understanding is that inactive memory is memory containing programs and data which you have quit. OS X keeps the memory incase you decide to restart the program. Because it is still in memory it can start it much quicker. You can see this in action by quitting a large program and restarting it. It should start much faster than it originally did.

Inactive memory does not suck up your memory though because OS X regards it as still available for programs to use, jsut at a lower priority than free memory. ie. if OS X needs memory for another program, it will allocate memory from the free area, then the inactive allocation. So when thinking about how much memory you have free for applications to use, inactive and free is combined.

As for swap, if a program is using it you should easily be able to tell by the amount of I/O going on and a noticable slow down.

If you really want to see whats going on I would suggest download iStat menus which is a really nice tool for seeing the internals of your system and display various instruments in the menu bar.

… set the minimum swapfile size …

dynamic_pager(8) Mac OS X Manual Page

With Terminal, a one-off command to convert a property list to a format that will be easily editable:

sudo plutil -convert xml1 com.apple.dynamic_pager.plist

Then if you're happy to edit with nano:

sudo nano /System/Library/LaunchDaemons/com.apple.dynamic_pager.plist

Use option -S to set a size in bytes, then save that property list and either:

• simply, safely, restart the Mac; or
• unload then load the daemon – but that may be risky (and I suspect that only a restart of the Mac will reap the potential benefits).

That's a single size for all files, and any use of option -S will cause dynamic_pager to not use variable sized paging files:

• we can not simply set a minimum – alone – amongst that set of variables.

… I want default allocate minimum 4GB …

Based on my tests with Mountain Lion, you might find that dynamic_pager will quietly fail to begin with a file that is so large.

Proceed with caution – pay attention to the actual size of swapfile0 and if it is zero bytes, then beware of inexplicable reductions to free space on the volume where the files are expected.

… at releasing will never release under 4GB size. …

Consider dynamic_pager option -L

If there are more than low-water-trigger bytes free in the external paging files, the kernel will coalese in-use pages and signal dynamic_pager to discard an external paging file. Low-water-trigger must be greater than high-water-trigger + filesize.