delphi - My program never releases the memory back. Why?

Question

I have a MDI program. When It starts it takes 2-3MB of RAM. Then, in this program I create about 260 MDI child windows (each has a TStringGrid, a bitmap and some other controls) and display some data. The application needs about 500MB to load all those windows. If I close each MDI child manually, the application still uses 160MB of RAM. Why it doesn't return to few MB of RAM? Should I worry about this? 160MB it is A LOT for a system that has only 1GB or RAM!!

Note: I use the WORKING SET column in Task Manager to see RAM statistics. Maybe I need a better tool to read the RAM utilization. (Private Working Set is just a bit smaller than Working Set).

This is not a leak!
FastMM (set on aggressive) indicates no memory leak when I close the program. See my Answer post for additional evidence that it isn't a leak.

I release stuff
Many people told me that closing a child window only hides it. I know that. I use "Action:= caFree" to actually release the forms. Each form is responsible for releasing the controls it holds.

Answer
I have found that FastMM is responsible for this. See the answer I posted below.

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Delphi 7, Win 7 32 bit
Similar posts:
Can memory be cleaned up?
When to call SetProcessWorkingSetSize? (Convincing the memory manager to release the memory)

Answer 1

Task Manager is not the right tool to detect memory leaks. Delphi allocates large blocks of memory and keeps them later for future use, so certain increase in allocated memory is expected even after you release all resources. Any other results (and more detailed answers) can be obtained only by using specialize memory analysis tools. AQTime is the first that comes to mind, or if you can find old but useful MemProof, it would help you a lot (MemProof is free and for memory analysis it's more handy than AQTime).