hello, what is the solution when safari tells me that my page uses a lot of memory

I have this problem too. If you open Activity Monitor you will probably see multiple processes called Safari Web Content (cached). The only way to put things back to normal again is to quit Safari and re-launch it.

Some web pages use a lot of resources. For them, Safari provides an informative message so that you may correlate your Mac's overall performance to what you're doing with it.