Jennifer Garner Takes Friendly Stroll with Ben Affleck's Mom

Jennifer Garner's not just good at getting along with her ex -- she's still totally cool with his mom too.

Jen was out for a walk Tuesday with Ben Affleck's mother, Chris, in Brentwood ... and they looked like 2 old friends yukkin' it up.

As we've reported, Jen and Ben have been doing the co-parenting thing like pros, while also having fun with their own friends. But clearly, for Jen anyway, family is family.

Besides ... always a good idea to keep Grandma happy.