Title: Mounting video ram on Linux

	Title: Mounting video ram on Linux
	Author: Solène
	Date: 10 February 2024
	Tags: linux
	Description: In this article, you will learn how to store data in your
	GPU memory on Linux

	# Introduction

	Hi, did you ever wonder if you could use your GPU memory as a mount
	point, like one does with tmpfs and RAM?

	Well, there is a project named vramfs that allows you to do exactly
	this on FUSE compatible operating system.

	In this test, I used an NVIDIA GTX 1060 6GB in an external GPU case
	connected with a thunderbolt cable to a Lenovo T470 laptop running
	Gentoo.

	vramfs official GitHub project page

	# Setup

	Install the dependencies, you need a C++ compiler and OpenCL headers
	for C++ (the package name usually contains "clhpp").

	Download the sources, either with git or using an archive.

	Run `make` and you should obtain a binary in `bin/vramfs`.

	# Usage

	It's pretty straightforward to use, as root, run `vramfs /mountpoint
	3G` to mount a 3 GB storage on `/mountpoint`.

	The program will stay in foreground, use Ctrl+C to unmount and stop the
	mount point.

	# Speed test

	I've been doing a simple speed test using `dd` to measure the write
	speed compare to a tmpfs.

	The vramfs mount point was able to achieve 971 MB/s, it was CPU bound
	by the FUSE program because FUSE isn't very efficient compared to a
	kernel module handling a file system.

	```
	t470 /mnt/vram # env LC_ALL=C dd if=/dev/zero of=here.disk bs=64k count=30000
	30000+0 records in
	30000+0 records out
	1966080000 bytes (2.0 GB, 1.8 GiB) copied, 2.02388 s, 971 MB/s
	```

	Meanwhile, the good old tmpfs reached 3.2 GB/s without using much CPU,
	this is a clear winner.

	```
	t470 /mnt/tmpfs # env LC_ALL=C dd if=/dev/zero of=here.disk bs=64k count=30000
	30000+0 records in
	30000+0 records out
	1966080000 bytes (2.0 GB, 1.8 GiB) copied, 0.611312 s, 3.2 GB/s
	```

	# Limitations

	I tried to use the vram mount point as a temporary directory for
	portage (the Gentoo tool building packages), but it didn't work due to
	an error. After this error, I had to umount and recreate the mount
	point otherwise I was left with an irremovable directory. There are
	bugs in vramfs, no doubts here :-)

	Arch Linux wiki has a guide explaining how to use vramfs to store a
	swap file, but it seems to be risky for the system stability.

	ArchWiki: Swap on video

	# Conclusion

	It's pretty cool to know that on Linux you can do almost what you want,
	even store data in your GPU memory.

	However, I'm still trying to figure a real use case for vramfs except
	that it's pretty cool and impressive. If you figure a useful
	situation, please let me know.