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Asked: 2026-05-18T20:09:19+00:00

I have a MDI program. When It starts it takes 2-3MB of RAM. Then,

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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.

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)

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1 Answer

  1. Editorial Team

    Answer:

    I just removed FastMM from my project and the program returned to few MB after freeing all those child windows. Many may argue that this is not a misbehavior and that FastMM is doing this in order to do some kind of kinky memory optimizations. They may be true. However, it may be good for MY application but it may not be good of other running applications.

    So, at least we know who causes this. I worried to a whole day that may program is leaking RAM like an old bucket. I am relieved now.

    UPDATE:

    To confirm that this behavior is generated by FastMM (as suggested by Barry Kelly) I created a second program that allocated A LOT of RAM. As soon as Windows ran out of RAM, my program memory utilization returned to its original value.
    (Note: I am not saying there is a bug in FastMM!)

    My program is not leaking. Problem solved.

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