When OS X (10.11 in my case) pops up a dialog saying the system has run out of application memory, what does this really mean? I've looked at this question, but my question is a bit more specific and not answered there.

It obviously doesn't simply mean the system is out of swap space, as I have over 500GB free, and I've seen this message when Activity Monitor reports 30GB or so used (I have 16GB of physical RAM).

I guess it has something to do with wired memory (pages that cannot be swapped out); normally, applications can't directly consume wired memory, but Parallels Desktop can and does, and it's when I'm using Parallels that I see the message.

But it isn't as simple as Parallels filling the whole memory with wired pages, either. When I've been able to check it, Activity Monitor has reported wired memory as high as 10GB, but that still leaves 6GB of physical memory free at the point when my system freezes up.

So, exactly what condition causes the system to give this message? Has the kernel hit some hard limit, or is it saying "I think there will be problems if I don't start suspending applications now"?

Update 12 Jan 2017

(This is still happening on macOS 10.12.2 Sierra)

I wrote a little app to continually display my system's use of wired memory. This routinely hits 70-80% when I'm using Parallels, but it seems like the "out of memory" error does not correlate with the amount of wired memory. I have got the error when that figure is below 20%.

  • This continues to drive me insane on a regular basis (now on 10.12). It's clearly not intended to be something most users will ever see; if I mistakenly close the dialog, macOS doesn't provide any other way to "resume" the paused apps. – bobtato Dec 4 '16 at 18:14

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