Benjamin Gaignard's Article on Linaro explains ION debugging as below (https://wiki.linaro.org/BenjaminGaignard/ion):
ION debug
ION provided a debugfs interface in /sys/kernel/debug/ion/ directory.
Each heap has it own debugfs entry where clients memory usage is displayed: /sys/kernel/debug/ion/<<heap name>>
$ cat /sys/kernel/debug/ion/ion-heap-1
client pid size
test_ion 2890 16384
Each client identify by pid have also a debugfs entry: /sys/kernel/debug/ion/<<pid>>
where memory usage displayed.
$ cat /sys/kernel/debug/ion/2890
heap_name: size_in_bytes
ion-heap-1: 40960 11
Easy enough to wrap a script and periodically monitor the output.