5 ms·

2^48 == 256TB. Anyone needs more than 256 Terabytes of RAM?

tpxl 6y ago
I am flirting with the idea of having 1TB of RAM on my servers as a small start-up. Having 256TB in 20 years seems reasonable.
- bitwize 6y ago
  You're gonna need at least that much to run the Electron apps of 20 years from now...
- rbanffy 6y ago
  A 128-bit CPU is not something I'd find outlandish in 20 years. OTOH, I was reading my e-mail on a 64-bit workstation (largely by accident, but still). In any case, I'd be quite surprised to see a 64-bit CPU doing such heavy lifting in 2040.
throwaway2048 6y ago
It ought to be enough for anyone
nnx 6y ago
Note this is for the virtual address space, not only for actual physical RAM. Having 256TB mmap’ed (to another kind of storage) does not seems totally out of reach.
- saagarjha 6y ago
  And in fact support for 5-level page tables was recently merged into the Linux kernel because people were coming close to this limit and needed more virtual address space.
- ljhsiung 6y ago
  True, but also note that a 52b mode (i.e. 12 bit tag) is also supported. I can't imagine anyone needing more than 4PB in the next 30 years, and the security gains now is (in my opinion) worth the potential refactoring in 30+ years that would be required.
  - StillBored 6y ago
    The couple year old power9 E980, can take 64T of ram. So there are people who have problems that need lots of addressable memory today. Even so, it wouldn't be that hard to actually build a system that could in theory try and map 4PB of storage via mmap today, its about 1/2 a rack of fairly common equipment. Given there are various companies selling 50T ssd (https://www.anandtech.com/show/11639/viking-ships-uhcsilo-ssds-50-tb-capacity-emlc-sas https://www.anandtech.com/show/11639/viking-ships-uhcsilo-ss...) its probably possible to do it in under 10U.
  - guenthert 6y ago
    Hmmh? A few years ago there were already a few sites with more than a PiB of storage total. I don't know of any which used some virtual memory or single address space scheme to access those, but I wouldn't want to rule it out.
cptnapalm 6y ago
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jcranmer 6y ago
It's 256TiB of virtual address space. If you include NVMe drives memory-mapped into the address space, hitting that cap is not entirely unreasonable. Intel added support for 5-level page tables (bumping virtual memory to 2^57 bytes) a few years ago: https://en.wikipedia.org/wiki/Intel_5-level_paging https://en.wikipedia.org/wiki/Intel_5-level_paging.

tpxl 6y ago

I am flirting with the idea of having 1TB of RAM on my servers as a small start-up. Having 256TB in 20 years seems reasonable.

bitwize 6y ago
You're gonna need at least that much to run the Electron apps of 20 years from now...
rbanffy 6y ago
A 128-bit CPU is not something I'd find outlandish in 20 years. OTOH, I was reading my e-mail on a 64-bit workstation (largely by accident, but still). In any case, I'd be quite surprised to see a 64-bit CPU doing such heavy lifting in 2040.

throwaway2048 6y ago

It ought to be enough for anyone

nnx 6y ago

Note this is for the virtual address space, not only for actual physical RAM. Having 256TB mmap’ed (to another kind of storage) does not seems totally out of reach.

saagarjha 6y ago
And in fact support for 5-level page tables was recently merged into the Linux kernel because people were coming close to this limit and needed more virtual address space.
ljhsiung 6y ago
True, but also note that a 52b mode (i.e. 12 bit tag) is also supported. I can't imagine anyone needing more than 4PB in the next 30 years, and the security gains now is (in my opinion) worth the potential refactoring in 30+ years that would be required.
- StillBored 6y ago
  The couple year old power9 E980, can take 64T of ram. So there are people who have problems that need lots of addressable memory today. Even so, it wouldn't be that hard to actually build a system that could in theory try and map 4PB of storage via mmap today, its about 1/2 a rack of fairly common equipment. Given there are various companies selling 50T ssd (https://www.anandtech.com/show/11639/viking-ships-uhcsilo-ssds-50-tb-capacity-emlc-sas https://www.anandtech.com/show/11639/viking-ships-uhcsilo-ss...) its probably possible to do it in under 10U.
- guenthert 6y ago
  Hmmh? A few years ago there were already a few sites with more than a PiB of storage total. I don't know of any which used some virtual memory or single address space scheme to access those, but I wouldn't want to rule it out.

cptnapalm 6y ago

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deleted 6y ago

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jcranmer 6y ago

It's 256TiB of virtual address space. If you include NVMe drives memory-mapped into the address space, hitting that cap is not entirely unreasonable. Intel added support for 5-level page tables (bumping virtual memory to 2^57 bytes) a few years ago: https://en.wikipedia.org/wiki/Intel_5-level_paging https://en.wikipedia.org/wiki/Intel_5-level_paging.