High Sierra Freezing - RAM Swap not working

Question

Level 1

7 points

High Sierra Freezing - RAM Swap not working

Hey,

i have a big Freezing Problem on my iMac 27" Late 2012 (8GB Ram) since i've installed High Sierra. The problem is that my mac freezes about 5 Times per day. I am running macOS on an external SSD per Thunderbolt.

I've tried many different things to solve this problem (e.g. VRam Reset, using another Cable, unplug all other Devices, reinstall macOS), but nothing helped.

Now i think i have the main issue. In case my Mac is going out of Memory the swapping mechanism is not working. The activity monitor shows exactly 0 Byte swapped. I used the same Python script on my iMac and on my MacBook as well. The iMac freezes and my MacBook is swapping about 6 GB.

I already tried deactivating the service by Terminal and activating it again. The Service is running, but it is not writing anything in a "swapfile -> /private/var/vm"

Is this a known issue? Is there anything i can do to fix this problem? I will not buy a ton of memory to solve this 🙂

Greetings

Posted on Dec 17, 2017 8:55 AM

Reply

Answer 1

Best reply

rezonanc

Level 1

9 points

Dec 20, 2017 1:17 PM in response to retone

I had the exact same issue. But the solution to this is even more crazy:

Try to execute the following:

sudo diskutil mount -mountPoint /private/var/vm disk2s4

disk2s4 (in my case) is an identifier to the VM (virtual memory) volume of APFS container, which could be located by diskutil apfs list.

So far this has been working for me well, if anyone knows how it would be possible to automate this after every reboot, that would be awesome to know!

Reply

Answer 2

John Galt

Level 10

140,872 points

Dec 17, 2017 2:40 PM in response to retone

The activity monitor shows exactly 0 Byte swapped.

That's OK since the screenshot shows an abundance of physical RAM. The swapfile was not being used because it was not yet required. Hover your cursor over the "Swap Used" text for an explanation of its purpose.

What do you do to recover from the freezes (in other words, is it necessary to force the Mac to shut down)?

Can you reproduce the freezing problem in "Safe Mode"?

Use safe mode to isolate issues with your Mac - Apple Support

Reply

Answer 3

retone Author

Level 1

7 points

Dec 17, 2017 2:40 PM in response to retone

Edit: Now I tried installing High Sierra on my Internal Slow HDD Drive. And now its working.

My Python script fills all the memory and the System is writing into a swap file. But on my external SSD this process is not working since High Sierra.

Reply

Answer 4

Jan 17, 2018 7:54 AM in response to retone

Same problem on a late 2011 27" iMac with an SSD in an external Thunderbolt 1 drive bay. Just executed the

sudo diskutil mount -mountPoint /private/var/vm disk2s4, and hey presto, swap is already being used!

Reply

Answer 5

hirokazu

Level 1

9 points

Feb 18, 2018 10:16 PM in response to rezonanc

Wow, thank you so much!

I am also booting off an external SSD (I realised after I bought this Mac that Fusion Drive is pretty much unusable garbage), and I was pulling my hair out trying to figure out why it'd crash twice a day.

Eventually I also narrowed it down to it crashing when too much RAM had been used, and then discovering that the swapfile isn't working.

My assumption is this is occuring because macOS uses a separate VM volume when the booting off an APFS volume, and for some reason this doesn't get detected in time to be mounted.

I guess the best solution is to put that command into a plist file and throw it into /Library/LaunchDaemons/ so that it gets mounted every time you boot up.

Otherwise a non-fudgy solution would probably be to reformat the drive back to HFS+ or create a Fusion Drive.

We should probably file a bug report with Apple unless they're already aware of this problem.

Reply

Answer 6

John Galt

Level 10

140,872 points

Dec 17, 2017 2:46 PM in response to retone

Certain model SSDs just don't work well with HS. Needless to say Apple is only interested in their own equipment. They don't test anything else.

Reply

Answer 7

retone Author

Level 1

7 points

Dec 20, 2017 1:18 PM in response to rezonanc

Thank you for your answer, i will try this the next time! My solution at the moment was creating a Fusion Drive. I don't know why, but swapping is working this way.

Reply