ramswaptmpfs
How to be sure that a tmpfs filesystem can only deal with physical and it's not using a swap partition on disk?
Since I have a slow HDD and a fast RAM, I would like, at least, giving higher priority to the RAM usage for swap and tmpfs or disabling the disk usage for tmpfs related mount points.
tmpfs is implemented as cache pages, so a low value for vm.swappiness will make tmpfs files more likely to be swapped out, since the system will favor stealing cache pages over application pages.
I figured I could just test it, so I ran:
sudo mount -o remount,size=2800M /run
Worked like a charm:
Filesystem Size Used Avail Use% Mounted on
tmpfs 2.8G 45M 2.7G 2% /run
So I filled it a bit:
fallocate -l 1G /run/test.img
fallocate -l 1G /run/test2.img
fallocate -l 500M /run/test3.img
Result:
Filesystem Size Used Avail Use% Mounted on
tmpfs 2.8G 2.6G 208M 93% /run
System is still up and running. Swap availability dropped, which proves it was used:
/runTotal swap is reduced by the amount taken by /run.
I'd test 10GB on a VM, because I don't know if the kernel will refuse the remount or just have an unexpected behavior.
I'm still looking for an actual answer, but the pragmatic way showed it works.
Best Answer
use ramfs instead of tmpfs. ramfs is a ramdisk (no swap) tmpfs can be both in your /etc/fstab:
edit the
sizeparameter to whatever you like but be careful not to exceed your actual amount of ram.NOTE: the use of a ramfs instead of tmpfs is not something i would recommend. you will find yourself experiencing stability issues if something happens and you write a ton of data to your ramdisk. you can NOT unallocate ram from a ramfs. once your ramdisk (all of your ram) is full your system will seize up. ram is volatile memory, meaning once it looses power all data is gone. so if your ramdisk fills up your ram and you crash you will never see what was on your ram disk again. unlike ramfs, tmpfs limits its size.