Large nfs write blocks/slows down other I/O operations

When performing a large write to a NFS share, then all other I/O operations towards this share is hung/slowed down until the large write operation is completed. In 20.04 this seems to be fixed. In 16.04 this was terrible and all other I/O operations was hung until the write had completed, in 18.04 this was slightly better, but still all I/O operations were slowed down significantly.

Is this a known issue? Would it be possible to backport whatever was changed between 18.04 and 20.04 to get the same fix in 18.04?

Example on how this is on 18.04:

# echo "baseline test - no write operation currently"
baseline test - no write operation currently
# time ls
... <directory listing omitted>

real 0m0.009s
user 0m0.005s
sys 0m0.001s
# dd if=/dev/zero of=test.img bs=1M count=10000 &
[1] 15489
# echo "write operation"
write operation
# time ls
... <directory listing omitted>

real 1m28.947s
user 0m0.000s
sys 0m0.970s
# 10000+0 records in
10000+0 records out
10485760000 bytes (10 GB, 9.8 GiB) copied, 90.6114 s, 116 MB/s

[1]+ Done dd if=/dev/zero of=test.img bs=1M count=10000

Here is the output from the 'mount'-command:

type nfs4 (rw,relatime,vers=4.2,rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=10.102.150.10,local_lock=none,addr=10.102.150.35)

With 20.04 this seems to be working just fine.