Many thanks for your answerThis topic has been discussed several times.
Having low free RAM is not an issue at all because it is directly managed and optimized by Linux in a very complex way.
If you try to continue free the memory, you just work against Linux which tries to optimize and speed up the system.
So, if you have 98% RAM memory used, it is a good thing.
Many thanksI installed also a SWAP file on a USB-Flash partition. Works fine with no side effects. If it is necessary or helps the performance?
It is hardly populated ever. Linux does a good job on memory management and removes things only when space is needed.
After doing an FTP for instance RAM is typically used to 98% or so. This is absolutely normal.