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0 pointsLegionMammal9782mo ago0 comments

I don't see how any amount of memory technology can overcome the physical realities of locality. The closer you want the data to be to your processor, the less space you'll have to fit it. So there will always be a hierarchy where a smaller amount of data can have less latency, and there will always be an advantage to cramming as much data as you can at the top of the hierarchy.

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adgjlsfhk12mo ago

while that's true, CPUs already have automatically managed caches. it's not too much of a stretch to imagine a world in which RAM is automatically managed as well and you don't have a distinction between RAM and persistent storage. in a spinning rust world, that never would have been possible, but with modern nvme, it's plausible.

bluGill2mo ago

Cpus manage it, but ensuring your data structures are friendly to how they manage caches is one of the keys to fast programs - which some of us care about.

adgjlsfhk12mo ago

Absolutely! And it certainly is true that for the most performance optimized codes, having manual cache management would be beneficial, but on the CPU side, at least, we've given up that power in favor of a simpler programming model.

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inkyoto2mo ago

«Memory technology» as in «a single tech» that blends RAM and disk into just «memory» and obviates the need for the disk as a distinct concept.

One can conjure up RAM, which has become exabytes large and which does not lose data after a system shutdown. Everything is local in such a unified memory model, is promptly available to and directly addressable by the CPU.

Please do note that multi-level CPU caches still do have their places in this scenario.

In fact, this has been successfully done in the AS/400 (or i Series), which I have mentioned elsewhere in the thread. It works well and is highly performant.

jason_oster2mo ago

> «Memory technology» as in «a single tech» that blends RAM and disk into just «memory» and obviates the need for the disk as a distinct concept.

That already exists. Swap memory, mmap, disk paging, and so on.

Virtual memory is mostly fine for what it is, and it has been used in practice for decades. The problem that comes up is latency. Access time is limited by the speed of light [1]. And for that reason, CPU manufacturers continue to increase the capacities of the faster, closer memories (specifically registers and L1 cache).

[1] https://www.ilikebigbits.com/2014_04_21_myth_of_ram_1.html

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adgjlsfhk12mo ago

bluGill2mo ago

Cpus manage it, but ensuring your data structures are friendly to how they manage caches is one of the keys to fast programs - which some of us care about.

adgjlsfhk12mo ago

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inkyoto2mo ago

«Memory technology» as in «a single tech» that blends RAM and disk into just «memory» and obviates the need for the disk as a distinct concept.

Please do note that multi-level CPU caches still do have their places in this scenario.

In fact, this has been successfully done in the AS/400 (or i Series), which I have mentioned elsewhere in the thread. It works well and is highly performant.

jason_oster2mo ago

> «Memory technology» as in «a single tech» that blends RAM and disk into just «memory» and obviates the need for the disk as a distinct concept.

That already exists. Swap memory, mmap, disk paging, and so on.

[1] https://www.ilikebigbits.com/2014_04_21_myth_of_ram_1.html

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