Thoughts about RAM and Storage Changes

My first Linux system in 1992 was a 386 with 4MB of RAM and a 120MB hard drive which (for some reason I forgot) only was supported by Linux for about 90MB. My first hard drive was 70MB and could do 500KB/s for contiguous IO, my first Linux hard drive was probably a bit faster, maybe 1MB/s. My current Linux workstation has 64G of RAM and 2*1TB NVMe devices that can sustain about 1.1GB/s. The laptop I’m using right now has 8GB of RAM and a 180GB SSD that can do 380MB/s.

My laptop has 2000* the RAM of my first Linux system and maybe 400* the contiguous IO speed. Currently I don’t even run a VM with less than 4GB of RAM, NB I’m not saying that smaller VMs aren’t useful merely that I don’t happen to be using them now. Modern AMD64 CPUs support 2MB “huge pages”. As a proportion of system RAM if I used 2MB pages everywhere they would be a smaller portion of system RAM than the 4KB pages on my first Linux system!

I am not suggesting using 2MB pages for general systems. For my workstations the majority of processes are using less than 10MB of resident memory and given the different uses for memory mapped shared objects, memory mapped file IO, malloc(), stack, heap, etc there would be a lot of inefficiency having 2MB the limit for all allocation. But as systems worked with 4MB of RAM or less and 4K pages it would surely work to have only 2MB pages with 64GB or more of RAM.

Back in the 90s it seemed ridiculous to me to have 256 byte pages on a 68030 CPU, but 4K pages on a modern AMD64 system is even more ridiculous. Apparently AMD64 supports 1GB pages on some CPUs, that seems ridiculously large but when run on a system with 1TB of RAM that’s comparable to 4K pages on my first Linux system. Currently AWS offers 24TB EC2 instances and the Google Cloud Project offers 12TB virtual machines. It might even make sense to have the entire OS using 1GB pages for some usage scenarios on such systems, wasting tens of GB of RAM to save TLB thrashing might be a good trade-off.

My personal laptop has 200* the RAM of my first Linux system and maybe 400* the contiguous IO speed. An employer recently assigned me a Thinkpad Carbon X1 Gen6 with an NVMe device that could sustain 5GB/s until the CPU overheated, that’s 5000* the contiguous IO speed of my first Linux hard drive. My Linux hard drive had a 28ms average access time and my first Linux hard drive probably was a little better, let’s call it 20ms for the sake of discussion. It’s generally quoted that access times for NVMe are at best 10us, that’s 2000* better than my first Linux hard drive. As seek times are the main factor for swap performance a laptop with 8GB of RAM and a fast NVMe device could be expected to give adequate performance with 2000* the swap of my first Linux system. For the work laptop in question I had 8G of swap and my personal laptop has 6G of swap which is somewhat comparable to the 4MB of swap on my first Linux system in that swap is about equal to RAM size, so I guess my personal laptop is performing better than it can be expected to.

These are just some idle thoughts about hardware changes over the years. Don’t take it as advice for purchasing hardware and don’t take it too seriously in general. Also when writing comments don’t restrict yourself to being overly serious, feel free to run the numbers on what systems with petabytes of Optane might be like, speculate on what NUMA systems in laptops might be like, etc. Go wild.

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