is there any memory leak when using arena parsing a lot of large string ?

[lzcchl]

I have searched for a lot of answers online, but still haven't solved the problem, the answer just like:
#6197
https://stackoverflow.com/questions/50414346/how-to-free-protocol-buffer-memory/50446245#50446245

I need free the memory eagerly, so I use arena. my test code is so small, you can find at here and have a quickly reading:
to_github.zip

you can run 4 step to run my example by run "bash step1.sh" "bash step2.sh" "bash step3.sh" "bash step4.sh", if you protoc version is large than 3.21, you should change the name "CMakeLists >= v3.22.txt" to "CMakeLists.txt".

the result just like:

Hello, Protobuf!
1
free_memory_gb: 12.7 GB

2
free_memory_gb: 11.6 GB

3
free_memory_gb: 11.8 GB

4
free_memory_gb: 11.8 GB

Goodbye, Protobuf!

memory leak happen!

but!!! if you change file src/ofs/ofs.cpp and rewrite msgTest.add_str(string("1234567891234567")); to msgTest.add_str(string("123456789123456")); , the length of the string has decreased from 17 to 16, and rerun bash, the result just like:

Hello, Protobuf!
1
free_memory_gb: 12.7 GB

2
free_memory_gb: 12.1 GB

3
free_memory_gb: 12.7 GB

4
free_memory_gb: 12.7 GB

Goodbye, Protobuf!

what's a big difference! at position 2, old free_memory_gb is 11.6 GB, new free_memory_gb is 12.1 GB, and at position3 the free_memory_gb return to 12.7 GB, there are no memory leak happen!

is there any bug at arena? or should I change some parameters to avoid memory leak? I have change ArenaOptions.start_block_size and ArenaOptions.max_block_size to larger valve, but it does't work, help! please, thank you.

[zenitaanders]