Jackson was recalled from Triple-A Sacramento on Sunday.
Jackson was sent to Triple-A on Sept. 22 but will rejoin the Giants after spending the 10-day minimum in the minors. The 34-year-old has a 3.74 ERA, 1.25 WHIP and 28:12 K:BB over 21.2 innings this season and has an outside chance at a spot on the postseason roster.