The factor 2 accounts for swap-out and swap-in. For example, a 100 MB process on a disk with ( L = 8 ) ms and ( R = 100 ) MB/s yields:
[ T_swap = 2 \times (L + \fracSR) ]
[ T_swap \approx 2 \times (0.008 + 1.0) \approx 2.016 \text seconds ] 9.5.6 Swapping