An ioctl() call to detect memory writes

Some GCs maintain "generations" of heaps. Allocations start in the 0th generation heap. If they have not been freed after X_0 GC scans of that heap they are migrated to the 1st-gen heap; if not freed after X_1 scans, migrate to 2nd-gen heap; and so on.

Each successive heap has a longer and longer scan time. I.e., X_0 < X_1 < ..., and X_i < X_(i+1) for all i in N_0. So young objects get checked quickly, longer lived objects get checked less and less.