How to measure total writes performed to SSD in Linux?

This values are hold in S.M.A.R.T attributes. You cat use smartctl command from smartmontools to get them.

UPD smartctl -A /dev/sda | grep -i 'media_wearout_indicator' | tr -s ' ' | cut -d' ' -f4-5 will output VALUE,WORST and THRESHOLD for Media_Wearout_Indicator. Note: for your device the attribute may have different name and threshold value, or may be unavailable at all. Depends on device vendor.