pt-online-schema-change crashes instance by allocating all available memory.

when i use pt-online-schema-change it crashes my ec2 instance (micro with 1gb ram, i even tried a small with 2gb). it gets so bad i don’t even have enough memory to reboot (not enough memory to sudo, and i have to stop the instance).

is there a way to limit max memory usage for this tool? it’s basically unusable for certain large tables.