[ilyt]

Use BIRD:

    bird> show memory 
    BIRD memory usage
    Routing tables:    262 MB
    Route attributes:  120 MB
    ROA tables:        192  B
    Protocols:         171 kB
    Total:             382 MB


    bird> show route count table r1
    906312 of 906312 routes for 906312 networks
    bird> show route count table r2
    903532 of 903532 routes for 903532 networks
    bird> 

routes in kernel will take less as you're only getting best one exported to kernel and no route attributes to hold