Question

I had an issue recently (see my last question) that led me to take a closer look at the memory management in my Delphi application. After my first exploration, I have two questions.

I’ve started playing with the FastMMUsageTracker, and noticed the following. When I open a file to be used by the app (which also creates a form etc…), there is a significant discrepancy between the variation in available virtual memory for the app, and the variation in “FastMM4 allocated” memory.

First off, I’m a little confused by the terminology: why is there some FastMM-allocated memory and some “System-allocated” (and reserved) memory? Since FastMM is the memory manager, why is the system in charge of allocating some of the memory?

Also, how can I get more details on what objects/structures have been allocated that memory? The VM chart is only useful in showing the amount of memory that is “system allocated”, “system reserved”, or “FastMM allocated”, but there is no link to the actual objects requiring that memory. Is it possible for example to get a report, mid-execution, similar to what FastMM generates upon closing the application? FastMM obviously stores that information somewhere.

As a bonus for me, if people can recommend a good reference (book, website) on the subject, it would also be much appreciated. There are tons of info on the net, but it’s usually very case-specific and experts-oriented.

Thanks!

PS: This is not about finding leaks, no problem there, just trying to understand memory management better and be pre-emptive for the future, as our application uses more and more memory.

Answer 1

Some of your questions are easy. Well, one of them anyway!

Why is there some FastMM-allocated
memory and some “System-allocated”
(and reserved) memory? Since FastMM is
the memory manager, why is the system
in charge of allocating some of the
memory?

The code that you write in Delphi is only part of what runs in your process. You use 3rd party libraries in the form of DLLs, most notably the Windows API. Anytime you create a Delphi form, for example, there are a lot of windows objects behind it that consume memory. This memory does not get allocated by FastMM and I presume is what is termed “system-allocated” in your question.

However, if you want to go any deeper then this very rapidly becomes an extremely complex topic. If you do want to go deeper into the implementation of Windows memory management then I think you need to consult a serious reference source. I suggest Windows Internals by Mark Russinovich, David Solomon and Alex Ionescu.