Gentoo tmpfs on GPU Ram disk?

nathanlkoch · Posted: Tue Feb 02, 2021 5:12 am Post subject: Gentoo tmpfs on GPU Ram disk?

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

DawgG · l33t Joined: 17 Sep 2003 Posts: 874

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

NeddySeagoon · Posted: Tue Feb 02, 2021 12:07 pm Post subject:

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.
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DawgG · l33t Joined: 17 Sep 2003 Posts: 874

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.
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Ant P. · Watchman Joined: 18 Apr 2009 Posts: 6920

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 · Posted: Tue Feb 02, 2021 7:11 pm Post subject:

Now I know.

Zucca · Posted: Tue Feb 02, 2021 7:37 pm Post subject:

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.
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nathanlkoch · Posted: Tue Feb 02, 2021 9:05 pm Post subject:

pjp · Administrator Joined: 16 Apr 2002 Posts: 20521

nick_gentoo · Tux's lil' helper Joined: 07 Jan 2019 Posts: 140

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 · Posted: Wed Feb 03, 2021 7:43 pm Post subject:

Zucca · Posted: Wed Feb 03, 2021 8:02 pm Post subject:

https://github.com/Overv/vramfs
Oh this is fun. :P
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nick_gentoo · Tux's lil' helper Joined: 07 Jan 2019 Posts: 140

Thank you for the pointers!

Zucca · Posted: Thu Feb 04, 2021 10:29 am Post subject:

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.
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