Re: Why is OS X swapping with inactive memory available?

• Subject: Re: Why is OS X swapping with inactive memory available?
• From: Jeff Stearns <email@hidden>
• Date: Thu, 29 May 2008 20:02:50 -0700
• Delivered-to: email@hidden
• Delivered-to: email@hidden

On May 29, 2008, at 7:07 PM, Terry Lambert wrote:

On May 29, 2008, at 2:11 PM, Dan Shoop wrote:

On May 28, 2008, at 3:36 PM, Thomas Backman wrote:

Nobody?
This is very annoying... I rebooted 40 minutes ago. Since then I started a VM with 640MB RAM (in VirtualBox, rather than VMware), iTunes, Firefox etc. Current RAM stats:
Free: 25MB
Inactive: 1.12GB
Wired: 891MB
Active: 1007MB
Page outs: 25MB (it stopped paging when I quit Firefox)

Why is it swapping with 37% of my total RAM inactive?! I just don't get it. Stuff starts beachballing at random, etc.
I'm starting to seriously consider switching to another OS because of this. I can't use virtual machines anymore, and that's not the only problem, either... Needless to say it happens without them, too, sooner or later... :(

I realize this isn't really the "OS X support" list, just figured people here might know what's going on.

Your presumptions about how VM [virtual memory] works on OS X are inaccurate, which is resulting in misconceived beliefs as to what occurring. You might consider reading Amit Singh's excellent Mac OS X Internals book.

As for your "beachballs", these are (most generally speaking) not caused by VM paging/swapping, but by other IO subsystem waits. Indeed I'm not even sure VM paging could ever incur a beachball. If you're seeing beachballs look for why your IO is stalling. "Spin Control" can help you here.

If you're using virtual machines, this can explain, perhaps, why you're seeing a high than normal incidence of beachballs since (a) your IO subsystem isn't 'real', and (b) you have other virtual machines competing for your real IO subsystem. Both of these could contribute your your observed waits.

Again, "Spin Control", the tool, can assist you in determining what these beachballs are caused by and could lead you to a solution.

And the "beach balls" are actually because the "are you alive?" messages being sent to the applications run loop by the window server (which is what controls the mouse curosor) are not responded to.

The "beach balls" are typically caused by doing blocking work in your application run loop, instead of marshalling that work off to another thread to get it completed there, instead. Because of that, the run loop is not reentered at the top often enough to respond to the events. So it's usually an indicator of an application design issue.

-- Terry

Pot, meet kettle.