What is that "theory"?  How are you comparing?

Yes, the current write performance of DCPMM is very bad, I look forward to its performance under TrueNAS SCALE, theoretically the performance in linux is twice as good as freebsd

Hmm. It works, but 8 times slower than mine at large I/Os.  Is that Intel Optane DIMM?  I've heard they should be slower on write, but never had a chance to measure.

now work 😉

/dev/pmem0
512 # sectorsize
270582935552 # mediasize in bytes (252G)
528482296 # mediasize in sectors
0 # stripesize
0 # stripeoffset
PMEM region 252GB # Disk descr.
E60A9A2579EB399E # Disk ident.
No # TRIM/UNMAP support
0 # Rotation rate in RPM

I/O command overhead:
time to read 10MB block 0.002218 sec = 0.000 msec/sector
time to read 20480 sectors 0.016406 sec = 0.001 msec/sector
calculated command overhead = 0.001 msec/sector

Seek times:
Full stroke: 250 iter in 0.000500 sec = 0.002 msec
Half stroke: 250 iter in 0.000486 sec = 0.002 msec
Quarter stroke: 500 iter in 0.000997 sec = 0.002 msec
Short forward: 400 iter in 0.000766 sec = 0.002 msec
Short backward: 400 iter in 0.000822 sec = 0.002 msec
Seq outer: 2048 iter in 0.001842 sec = 0.001 msec
Seq inner: 2048 iter in 0.001862 sec = 0.001 msec

Transfer rates:
outside: 102400 kbytes in 0.013630 sec = 7512839 kbytes/sec
middle: 102400 kbytes in 0.013790 sec = 7425671 kbytes/sec
inside: 102400 kbytes in 0.013994 sec = 7317422 kbytes/sec

Asynchronous random reads:
sectorsize: 1425829 ops in 3.000028 sec = 475272 IOPS
4 kbytes: 864612 ops in 3.000029 sec = 288201 IOPS
32 kbytes: 945080 ops in 3.000400 sec = 314985 IOPS
128 kbytes: 164956 ops in 3.002401 sec = 54941 IOPS

Synchronous random writes:
0.5 kbytes: 2.0 usec/IO = 241.0 Mbytes/s
1 kbytes: 2.1 usec/IO = 466.8 Mbytes/s
2 kbytes: 2.3 usec/IO = 848.2 Mbytes/s
4 kbytes: 2.6 usec/IO = 1510.5 Mbytes/s
8 kbytes: 5.1 usec/IO = 1544.3 Mbytes/s
16 kbytes: 10.8 usec/IO = 1452.0 Mbytes/s
32 kbytes: 20.8 usec/IO = 1503.5 Mbytes/s
64 kbytes: 37.7 usec/IO = 1658.9 Mbytes/s
128 kbytes: 79.2 usec/IO = 1577.3 Mbytes/s
256 kbytes: 157.2 usec/IO = 1590.8 Mbytes/s
512 kbytes: 310.1 usec/IO = 1612.5 Mbytes/s
1024 kbytes: 665.0 usec/IO = 1503.7 Mbytes/s
2048 kbytes: 1364.2 usec/IO = 1466.0 Mbytes/s
4096 kbytes: 2800.3 usec/IO = 1428.4 Mbytes/s
8192 kbytes: 5639.6 usec/IO = 1418.5 Mbytes/s

I've reproduced the issue on my Supermicro X11DPI-NT board.  I've found that if I disable ACPI NUMA support in BIOS ACPI still reports non-existing now NUMA domain 1 for some NVDIMMs.  The patch I've committed should properly handle NUMA domain reporting.

Please update to 12.0-U1 and unpack the attached kernel instead of the default one into /boot.  Make sure to create boot environment in case something go wrong and you have to revert back.