Why is the memory usage of nebula-storage so high?

[jzx1000]

My Nebula configuration includes 100 graph spaces, each with very few vertices and edges.
Each graph space has a replica count of 1 and a partition count of 60.
I haven't done anything else, but the memory usage of nebula-storage has been steadily increasing, reaching over 25 GB.

What could be the reason for this? Is it a memory leak? Do I need to adjust some configurations?
Or how can I configure it to keep memory usage stable within a certain range?