A method for minor garbage collection involves marking cards as clean, where the cards designate ranges of memory locations in a shared older generation, marking a card as dirty to obtain a dirty card when a reference field of an object is modified, where the object is allocated in one of multiple promotion areas, where the promotion area is used to promote objects to the shared older generation only for a single task, and where the card designates the reference field's memory location, examining the promotion areas and the cards to identify a region of the dirty card overlapping the promotion area, where promotion areas associated with other tasks are ignored, scanning the region of the dirty card overlapping the promotion area to identify roots of live young objects associated with the single task, and freeing a young object associated with the single task not identified as live during scanning.