The initial release was really underwhelming, given the hype around this. So my personal (uninformed) expectations is just incremental improvement to the initial product.
Intel’s Plans for 3DXP DIMMs Emerge
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Re: Intel’s Plans for 3DXP DIMMs Emerge
#22The initial release was really underwhelming, given the hype around this. So my personal (uninformed) expectations is just incremental improvement to the initial product.
Moving 3D XPoint memory from the peripheral IO bus to the memory bus is way more than an incremental improvement.
Re: Intel’s Plans for 3DXP DIMMs Emerge
#23It seems obvious in retrospect, but persistent memory adds a pretty exciting new advantage for persistent data structures. Another thought: As potentially paradigm changing technology like this becomes available will it ever make sense to redesign the OS?
Seriously, yes. If there was ever a time to rethink OS design, surely this is it.
That being said, operating systems like Linux tend to capture most of the value from these kind of advances - often by dint of being able to simply 'get out of the way' if a sufficiently important user space process wants access to the device.
But one would suspect that things have changed sufficiently from the 1970s to warrant a ground-up rethink. Core counts, distributed systems (the Plan 9 folks already too a swing at this in the 90s), nearly ubiquitous graphics/GPGPU accelerators, persistent memory, nearly ubiquitous access to 64-bit address spaces (at least for desktop and most phones) - you'd think something would change about design. I don't work in the area so I don't know what that is...
Re: Intel’s Plans for 3DXP DIMMs Emerge
#24Why can't we just put a battery onto DRAM that maintains state if the power goes out, and be done with it?
DRAM is not that dense; you can fit 128 GB of DRAM or 512 GB of XPoint on a DIMM. XPoint is also supposed to be cheaper than DRAM.
Re: Intel’s Plans for 3DXP DIMMs Emerge
#25It seems obvious in retrospect, but persistent memory adds a pretty exciting new advantage for persistent data structures. Another thought: As potentially paradigm changing technology like this becomes available will it ever make sense to redesign the OS?
I would also think, OSes that tend to emphasize their primary file systems as 'the distributed memory', like DragonFly BSD -- would benefit significantly.
I am speculating, of course, but the whole Hammer 2 design of DF BSD emphasizes cross-machine 'database-like' file system, with built-in transparent state snapshots, state-branches, etc. [1].
So with this new type of persistent storage, DF's Hammer2 could erase the difference between 'persistent state' and in-memory-only state.
Therefore eliminating the need for reconciliations, application-specific backups, and application-specific distributed architectures.
Re: Intel’s Plans for 3DXP DIMMs Emerge
#26It seems obvious in retrospect, but persistent memory adds a pretty exciting new advantage for persistent data structures. Another thought: As potentially paradigm changing technology like this becomes available will it ever make sense to redesign the OS?
Probably the optimal use of this technology is databases, since they rely most on random access to large persistent data.
Any operating system that's designed around this technology is probably going to look like a database.
Basically, boot to Postgres and all "files" are now SQL tables, stored in NVDIMM. Indexes are in DRAM, and critical nodes are in cache.
All data (system and user) is organized and opinionated: All photos are in a photo database, with tables for IPTC metadata. All music. All executable files. If you're browsing the web, it'll probably cache data in local SQL tables. etc..
I can envision using SQL stored procedures as actual apps, perhaps with an API to access graphics hardware, network, sound, etc..
Re: Intel’s Plans for 3DXP DIMMs Emerge
#27I guess in a theoretical NVM-only system you could pull the plug at any time, and instantly resume it when the power is back on? If I'm reading right though the latency of 3DXP is somewhere in the 10-20us ballpark, still 100-1000x slower than DRAM.
Re: Intel’s Plans for 3DXP DIMMs Emerge
#28It seems obvious in retrospect, but persistent memory adds a pretty exciting new advantage for persistent data structures. Another thought: As potentially paradigm changing technology like this becomes available will it ever make sense to redesign the OS?
I used to think so - once you have persistent primary memory, you can install operating systems and applications directly into primary memory, so there's no longer any point in having a distinction between "install" and "run/boot".
However, iOS and Android have shown that it's possible to do away with this distinction even with a traditional OS running underneath. So I now tend to think that instead what will happen is more continual evolutionary changes at the OS level to work better in a "boot once" environment, rather than a revolution.
Re: Intel’s Plans for 3DXP DIMMs Emerge
#29Why can't we just put a battery onto DRAM that maintains state if the power goes out, and be done with it?
Because the power consumption to keep DRAM refreshed is fairly high so you'd need a pretty big battery, and because it would still be more expensive than 3DXP. It's just not practical for most use cases.
I figured that, but can we have some numbers here?
Re: Intel’s Plans for 3DXP DIMMs Emerge
#30I guess in a theoretical NVM-only system you could pull the plug at any time, and instantly resume it when the power is back on? If I'm reading right though the latency of 3DXP is somewhere in the 10-20us ballpark, still 100-1000x slower than DRAM.
Yes but it's also cheaper than DRAM.
You could resume after pulling the plug as long as things are consistent. If you commit data in the wrong order you could have trouble!