Yes yes, the increase does indeed occur at the time of the backup.
I just wanted to understand how you actually measure RAM usage?
Depending on the method used, you won’t necessarily see the RAM being « freed » after the backup, and that’s perfectly normal on Linux.
Some tools show the total RAM used by including the cache and buffers, which can give the impression that no RAM has been freed, whereas the RAM is indeed freed and immediately reusable.
But it’s also possible that there’s an issue with memory being released — that’s why the technical details would help a lot 