Comment 13 for bug 1333294

I can confirm the same problem for me (however the system in question is actually Fedora 27, but no other online source provided a solution except for this bug report):

kernel: 4.10.10 SMP PREEMPT i686 (32bit)
compiled with gcc_7.3.1

started with write speeds at around 180 MB/s and within minutes would slow down and stabilize at 3 MB/s

# echo 3 > /proc/sys/vm/drop_caches

did not work, but

# sysctl -w vm.highmem_is_dirtyable=1

worked like a charm!

I will try to see if I can test some of the other kernels as mentioned above (64bit, versions above 4.13) and see if those manifest the same issues.

Thanks Norbert (nrbrtx)!