Maximum number of threads per process in Linux?

Question

What is the maximum number of threads that can be created by a process under Linux?

How (if possible) can this value be modified?

Answer 1

proper 100k threads on linux:

ulimit -s  256
ulimit -i  120000
echo 120000 > /proc/sys/kernel/threads-max
echo 600000 > /proc/sys/vm/max_map_count
echo 200000 > /proc/sys/kernel/pid_max 

 ./100k-pthread-create-app

2018 update from @Thomas, on systemd systems:

/etc/systemd/logind.conf: UserTasksMax=100000