Persistent memory (was Re: [9fans] venti /plan9port mmapped)

[arnold@skeeve.com]

Shawn Rutledge <lists@ecloud.org> wrote:

> I’ve been wondering why it’s still so rare to map persistent storage
> to memory addresses, in hardware.  It seemed like Intel Optane was
> going to go there, for a while, then they just gave up on the idea.

Because Intel doesn't understand any kind of product except CPUs. :-(

> I think universal memory should happen eventually; and to prepare for
> that, software design should go towards organizing data the same in
> memory as on storage: better packing rather than lots of randomness in
> the heap, and memory-aligned structures. Local file I/O might become
> mostly unnecessary, but could continue as an abstraction to organize
> things in memory, at the cost of having to keep writing I/O code.  So if
> that’s where we are going, mmap is a good thing to have.  But yeah,
> maybe it’s more hassle as an abstraction for network-attached storage.

A web search shows that there are several options for peristent memory
allocators, many of which I didn't know about. However, gawk has
been using one for a few years. See https://dl.acm.org/doi/10.1145/3643886
and https://web.eecs.umich.edu/~tpkelly/pma/. It's built on top of
mmap() and only for 64-bit *nix systems.

For the short instructions on using it, see
https://www.gnu.org/software/gawk/manual/html_node/Persistent-Memory.html.
For more details, see
https://www.gnu.org/software/gawk/manual/pm-gawk/pm-gawk.html.

Arnold

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