Prevent process pages from being swapped

[Atrate]

Closes: #31

Seems to work, tests done:

1. Create high memory pressure via stress --vm 20 --vm-bytes 1024M --vm-hang 1
2. Set swappiness to max echo "200" | sudo tee /proc/sys/vm/swappiness
3. Launch vramfs with and without the fix (in this case with root privileges and without, as it can't protect pages without root)
4. Check the resulting processes /proc/<PID>/status

Results:

1. Process with protection:

VmSwap:	       0 kB

2. Proces without protection:

VmSwap:	       784 kB

Signed-off-by: Atrate [email protected]

[Atrate]

@Overv Having carried out simple tests as outlined in OP, this PR is now ready for review.

[Overv]

I'll review this once I find some time.

[Overv]

I see that you deleted your comment about other processes that may still be swapped out. Was that a mistake or is that still a concern after this PR?

[Atrate]

I traced the source of that particular freezing to the fact that I was using linux-hardened, not that I was swapping on VRAM. Other processes being swapped out should technically not be a problem, as drivers are kernel threads, which AFAIK can't be swapped out, but once I confirm that the kernel I am using right now is fully stable, I'll go back to using swap on VRAM and watching for freezes.

[Overv]

Cool 👍