RE: [PATCH] mm: Introduce kernelcore=reliable option

From: Luck, Tony
Date: Fri Oct 30 2015 - 15:42:24 EST

> If each memory controller has the same distance/latency, you (your firmware) don't need
> to allocate reliable memory per each memory controller.
> If distance is problem, another node should be allocated.
> the behavior(splitting zone) really required ?

It's useful from a memory bandwidth perspective to have allocations
spread across both memory controllers. Keeping a whole bunch of
Xeon cores fed needs all the bandwidth you can get.

Socket0 is also a problem. We want to mirror <4GB addresses because
there is a bunch of critical stuff there (entire kernel text+data). But we
can currently only mirror one block per memory controller, so we end up
with just 2GB mirrored (the 2GB-4GB range is MMIO). This isn't enough
for even a small machine (I have 128GB on node0 ... but that is really the
bare minimum configuration ... 2GB is only enough to cover the "struct
page" allocations for node0). I really have to allocate some more mirror
from the other memory controller.


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