Gentoo tmpfs on GPU Ram disk?

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nathanlkoch · Post by **nathanlkoch** » Tue Feb 02, 2021 5:12 am

Could one setup distc with portage's directory on a gpu ramdisk for extremely fast builds? Has anyone done it before?

DawgG · Post by **DawgG** » Tue Feb 02, 2021 10:01 am

it can certainly be done: mount the tmpfs and set portage_tmpdir (look up the exact variable name in make.conf) to that.
i wouldn't expect

extremely fast builds

though because on systems accessible to us mere mortals usually disk-io or, in this case, ram-speed isn't the limiting factor when compiling but cpu power. i ususally keep portage_tmpdir in ram and i cannot say there is a noticeable speed increase when building. just give it a try!
GOOD LUCK!

Post by **NeddySeagoon** » Tue Feb 02, 2021 12:07 pm

DawgG,

There isn't a speed improvement for the portage build space in RAM.
When you have the RAM for it. the kernel virtual memory system keeps the build products in the disk cache. They are never flushed as there is no demand on RAM.
You just get a lot of writes to disk that are never read. Putting the portage build space in RAM saves these writes. That's a good thing on SSD.
It saves bus bandwidth but thats not a speed improvement that you would notice.

As to using the RAM on a GPU, it will be slower than main memory because the interface is not designed to access filesystems.

DawgG · Post by **DawgG** » Tue Feb 02, 2021 1:16 pm

NeddySeagoon,
you are right - THX for the info.
one other main reason for doing this is that it "cleans" the build-dir on every remount/reboot.

Ant P. · Post by **Ant P.** » Tue Feb 02, 2021 3:40 pm

A PCIe 4.0 x16 card will give you a maximum of 31GB/s bandwidth. Dual-channel DDR4 at its slowest rated speed is faster than that. Same goes for PCIe/DDR 3 and most of DDR 2 as well.

You won't get extremely fast builds, you'll get extremely hot builds.

nathanlkoch · Post by **nathanlkoch** » Tue Feb 02, 2021 7:11 pm

Now I know.

Website · Post by **Zucca** » Tue Feb 02, 2021 7:37 pm

Fun fact: there was a driver that made possible to use GPU ram as swap. It could be useful on some laptops with dedicated gpu.

nathanlkoch · Post by **nathanlkoch** » Tue Feb 02, 2021 9:05 pm

Zucca wrote:Fun fact: there was a driver that made possible to use GPU ram as swap. It could be useful on some laptops with dedicated gpu.

Neat-o.

Post by **pjp** » Tue Feb 02, 2021 9:12 pm

Zucca wrote:Fun fact: there was a driver that made possible to use GPU ram as swap. It could be useful on some laptops with dedicated gpu.

Also to not use system RAM and still preserve solid-state devices.

nick_gentoo · Post by **nick_gentoo** » Wed Feb 03, 2021 12:20 pm

Hi, I understand why the GPU ramdisk is not such a good idea, but the geek in me is asking: HOW exactly is that done?

nathanlkoch · Post by **nathanlkoch** » Wed Feb 03, 2021 7:43 pm

nick_gentoo wrote:Hi, I understand why the GPU ramdisk is not such a good idea, but the geek in me is asking: HOW exactly is that done?

https://www.youtube.com/watch?v=sdlerQmeZds
https://www.reddit.com/r/pcmasterrace/c ... _gpu_vram/

Website · Post by **Zucca** » Wed Feb 03, 2021 8:02 pm

https://github.com/Overv/vramfs
Oh this is fun. :P

nick_gentoo · Post by **nick_gentoo** » Thu Feb 04, 2021 9:49 am

Thank you for the pointers!

Zucca wrote:Oh this is fun.

Yes, indeed

Website · Post by **Zucca** » Thu Feb 04, 2021 10:29 am

Now... Do I spare on RAM next time and invest in a pro GPU that has lots of vRAM?

Joking.

A little off-topic, but I have been looking at those WAM (Write acceleration module) cards as a faster swap device. Still buying more RAM makes more sense, obviously. But a PCIe card filled with cheap DDR3 memory is an interesting concept.