Freeing memory would require that there be an entirely empty page. Each page holds 13-14 objects (4k/300). The chances that 13 consecutive objects were in the

Freeing memory would require that there be an entirely empty page. Each page holds 13-14 objects (4k/300). The chances that 13 consecutive objects were in the 5% (assuming independent, random distribution) is 1 in 20^13, putting the expected number of empty pages well below 1. You have to migrate much more data before you can hope to see page-size holes.