If your Android device (4.3+) is slow as hell due to I/O waiting. Try this command which will force an fstrim.

am broadcast -a android.intent.action.ACTION_IDLE_MAINTENANCE_START

$ adb logcat | grep -i fstrim
 I/fstrim ( 119): Starting fstrim work...
 I/fstrim ( 119): Invoking FITRIM ioctl on /cache
 I/fstrim ( 119): Trimmed 447336448 bytes on /cache
 I/fstrim ( 119): Invoking FITRIM ioctl on /data
 I/fstrim ( 119): Trimmed 1194917888 bytes on /data
 I/fstrim ( 119): Finished fstrim work.