Why do nvs_flash_init and nvs_flash_init_partition take so much RAM?

[A6ESPF]

I have three NVS partitions, the first one is the default partition with 20 KiB size, the second and third ones are the same size (352 KiB). When I run nvs_flash_init, which initializes the default NVS partition, my heap is reduced by ~1.2 KiB, and when I run nvs_flash_init_partition for the two remaining partitions, my heap is further reduced by ~15KiB. It seems like nvs_flash_init* heap usage is proportional to the size of the NVS partition. Why is that so?