eMMC support & concerns

[Matthew Dillon]

Well, the first question is whether DFly can even probe the eMMC.  If you
can boot DFly from a usb stick and play with it from there, that's the
easiest way to check which resources are or are not supported.

We do have eMMC support and generally speaking your research is correct...
it is not a good idea to do heavy writing to eMMC, and the transfer rate is
very slow (it is literally a serial protocol that runs in the megabit range
rather than the gigabit range).  eMMC is suitable for booting systems and
reading, but writing should be minimized.   eMMC performance is poor
regardless of the operating system.  That said, operating systems like
Linux or the BSDs will extensively cache read data in memory so it is
possible to have decent responsiveness.

Beyond that, DFly can be made relatively eMMC-friendly by not configuring
any swap space (unless absolutely necessary), and using tmpfs filesystems
for /tmp and /var/tmp (also /var/run/shm but that is typically already
tmpfs based).  Hammer2 should work fairly well with it.  The larger the
eMMC drive, the better.

-Matt
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