The New Hotness

Depending on a solid model’s complexity, OpenSCAD will sometimes chew through system memory, consume the entire swap file, and then fall over dead. In an attempt to work around that situation, I recently jammed a 32 GB USB drive into the back of the box, turned it into a swap device, and then told the kernel to back off its enthusiasm for swapping.

Format the USB drive as a swap device:

sudo mkswap /dev/sd??   #--- unmount it before you do this!
Setting up swapspace version 1, size = 31265292 KiB
no label, UUID=0f559a8c-67b7-4fa3-a709-17aeec3104c4

Add it to /etc/fstab and set swap priorities:

# swap was on /dev/sdb3 during installation
UUID=e8532714-ad80-4aae-bee7-a9b37af63c8c none  swap sw,pri=1	0 0
UUID=0f559a8c-67b7-4fa3-a709-17aeec3104c4 none	swap sw,pri=5	0 0

Turn it on:

sudo swapon -a

Following those directions, dial back the kernel’s swappiness and limit the file cache growth:

sudo sysctl -w vm.swappiness=1
sudo sysctl -w vm.vfs_cache_pressure=50

Those commands now live in /etc/sysctl.d/99-swappiness.conf:

cat /etc/sysctl.d/99-swappiness.conf
# Improve responsiveness by reducing cache swapping
vm.swappiness=1
vm.vfs_cache_pressure=50

For whatever reason, WordPress turns underscores into blanks, so those obvious typos aren’t, really.

And then it should Just Work.

The box has 4 GB of RAM and, under normal circumstances, doesn’t swap at all, so I expect the USB drive should kick in only for extreme OpenSCAD models. The swappiness tuning should help during ordinary operation with large file operations.

I have no results to report, but if something blows up, I know what changed…