[BUG] TWRP/CWM flashable zip not work.

I make flashable zip. system large is 650mb. i try install with twrp 3.1. I get error on step "INSTALLING rootfs...", in log i see "tar -xz rootfs.tar.gz /system KILLED" i see error about 10 second on start extracting rootfs. I get this error,because my RAM(1 GB)is very small(i see it in output of df command, i run it before start flashing and in time of flashing).