What is the meaning of message 'XXX used greatest stack depth: XXX bytes left' ?

Issue

• In /var/log/dmesg, following log messages were observed :

async/0 used greatest stack depth: 5568 bytes left
mknod used greatest stack depth: 5168 bytes left
mount used greatest stack depth: 5000 bytes left
loadkeys used greatest stack depth: 4888 bytes left
modprobe used greatest stack depth: 3968 bytes left
modprobe used greatest stack depth: 3888 bytes left
load_policy used greatest stack depth: 3056 bytes left
system-setup-ke used greatest stack depth: 3024 bytes left
ip used greatest stack depth: 2960 bytes left
flush-253:6 used greatest stack depth: 2472 bytes left
updatedb used greatest stack depth: 2208 bytes left