I'm using Open MP with Fortran 08 (compiled with GFortran) to create nested parallel regions (in my case, a 3-level nest). Before running my executable, I set some Linux environment variables to facilitate this nesting structure. In particular, I set OMP_NESTED=True, OMP_MAX_ACTIVE_LEVELS=3, OMP_NUM_THREADS=2,7,1, and OMP_STACKSIZE=4g.

My issue is that I think OMP_STACKSIZE sets the stack size of each thread, regardless of which level of the nested parallel region the thread is in. I have set the stack size high, since the first-level threads need a large amount of stack memory. However, the second- and third-level threads do not need nearly this much stack memory. Is there any way to set different stack sizes for different parallel regions? I haven't yet found a method using either Linux environment variables or the OMP libraries within Fortran.