What does kstat -p ::zfs_file_data:mem_total represent?
What does kstat -p ::zfs_file_data:mem_total represent? 
kstat -p | egrep 'zfs_file_data:mem_inuse|zfs_file_data:mem_total'
vmem:36:zfs_file_data:mem_inuse 8691646464
vmem:36:zfs_file_data:mem_total 50897879040
echo "::kmastat"| sudo mdb -k seems to indicate a total number of bytes":
echo "::kmastat"| sudo mdb -k | egrep '^cache|^name|^--------------|^zfs_file_data|^vmem'
...
vmem                          memory      memory     memory     alloc alloc
name                          in use       total     import   succeed  fail
------------------------- ---------- ----------- ---------- --------- -----
zfs_file_data             8691646464B 50897879040B         0B      8357     0
...
but the number is several times the size of physical memory:
echo "::memstat"| sudo mdb -k
                0      
            