The Packers structured Perry's most recent contract, which contained an $18.5 million signing bonus, so that they could move on after the 2018 season and actually gain salary-cap space. Perry is due a $4.8 million roster bonus if he's on the team on the third day of the league year in 2019, so if the Packers cut him before that March date they would wipe that and his $5.2 million base salary off their cap.
They would have to count the remaining prorated portion of his signing bonus against their cap, but could defer some of that by designating him as a June 1 cut. If they cut him without the June 1 designation, they would save $3.6 million off their 2019 cap. If they used that designation, they would save $11.1 million.