Messages in this thread | | | Date | Mon, 2 Jun 2008 21:10:27 +0000 | From | Rick van Rein <> | Subject | Re: Future Linux on Bistable Storage |
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Hello,
Thanks for your responses. You convinced me I/O initiatilisation cannot be improved upon.
> unless there has been a breakthrough that I haven't heard about (always > possible) I seriously doubt that this is the case.
Oh wait... I'm talking of upcoming technologies, not established ones!
> the alternate technologies that I have heard about are either _far_ less > dense then DRAM (similar to static ram) or require erasing in blocks > (similar to flash).
NanoRAM for one sounds like it can achieve very high densities and high speeds in coming years. A slideshow from a researcher gives numbers:
http://www.imechanica.org/files/Proposal-MNRAM.pdf
100 GHz speeds, 100 T/cm2 -- and it's all bistable so no power is consumed to keep it going, as is a limitation with DRAM. With a cm2 of that I don't think we'd care for a HDD or for DRAM anymore.
> Perhaps one of the more key stepping stones here is execution in place > (XIP) support [...] Maybe [...] we should consider XIP-for-ramdisk > (rather than ROM/flash).
That's the sort of thing I was hoping to spark -- I hadn't seen XIP but it does sound like a limited form of the kind of thing that would integrate memory/disk into one large bowl of bits. Thanks for the pointer!
> Anyway, from a mmap() perspective, we'd be logically merging the > filesystem and pagecache layers and losing a layer of physical > indirection.
Something like that... a smooth exchange between memory pages and disk pages, where it would even be possible for a page to be part of both, a bit like XIP indeed.
> One major difference between disk and RAM is the tradeoffs between size, > speed, and price. It's highly unlikely that any one technology will ever > beat all others in both of the usage patterns which are normal for RAM and > disk in devices considered by their users to be "computers".
I beg to differ. If the numbers above are anything to go on, that is. We have a tendency to think of DRAM as something that can grow without bounds, but its power consumption and consequential dissipation due to refreshing do limit it, for example when applied in a mobile device.
Refreshes occur ~1000 times a second for all cells in DRAM, AFAIK. That's rather a lot of data being read and rewritten each second! No wonder the chips heat up, and consequently cannot be stacked to form a cubic memory structure.
> I think current ramdisk code skips [buffering disk blocks].
That'd help, but I'm not sure the concepts of memory and ramdisk should be kept separate if this architecture I am thinking of would come through.
You have helped to answer my question, whether Linux was ready for the architecture that I talked about: it already contains seedlings for its support, so it does not seem to conflict with Linux' major architecture. That's good news!
Thanks,
Rick van Rein GroenGemak
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