As an alternative, we might use the "memmap=nn[KMG]!ss[KMG]" [1] parameter
to mark some memory as protected.
That memory can then be configured as devdax device and online to
ZONE_MOVABLE (dev/dax).
[1] https://docs.pmem.io/persistent-memory/getting-started-guide/creating-development-environments/linux-environments/linux-memmap
I've previously been reconfiguring devdax memory like this:
ndctl create-namespace --reconfig=namespace0.0 -m devdax -f
daxctl reconfigure-device --mode=system-ram dax0.0
Is this how you've been doing it, or is there something else I should
consider?
No, exactly like that.
I just sent mail to Michal outlining my use case, hopefully it makes sense.
Yes, thanks for sharing, I'll dig deeper into that next.
I had thought about using 'memmap=' in the first kernel and the worry was that
I'd have to support many different machines with different memory
configurations, and have to hard-code memory offsets and lengths for the
various memmap= kernel command line parameters.
Indeed.
If I can make ZONE_MOVABLE
work that's preferable because the kernel will choose the correct usermem-only
region for me, and then I can just use that region for the crash kernel and
3rd kernel boots.
It really sounds like you might be better off using CMA or
alloc_contig_pages().
The latter is unreliable, though, and the memory cannot be used for
other purposes once alloc_contig_pages() succeeded
See arch/powerpc/platforms/powernv/memtrace.c one one user that needs to
set aside a lot of memory to store HW traces.
--
Cheers,
David / dhildenb
