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I've been tracking down a few memory leaks in my application. It's been a real pain, but I've finally tightened everything up. However, there's one bit of Windows memory management that is confusing me. Here is a printout of the app's memory usage over time...
Time PrivateMemorySize64 WorkingSet64
20:00:36 47480, 50144
20:01:06 47480, 50144
20:01:36 47480, 50144
20:02:06 47480, 149540
20:02:36 47480, 149540
20:03:06 47480, 149540
The working set jumped from 49 MB to 146 over a span of 30 seconds. This happened overnight as the application was basically doing nothing.
The working set (which is what task manager shows me) seems to be able to be influenced by other applications such as debuggers (as I learned while looking for memory leaks). After reading the documentation on what Working Set is, I still don't have a good understanding.
Any help is appreciated.
Update: Thanks to some links from responders as well as some additional searching, I have a better understanding on how a separate process can cause my process' working set to grow. Good to know that a spike in the working set is not necessarily an indication that your app is leaking... Further reason to not rely on Task Manager for memory evaluation :)
Helpful links:
A few words on memory usage or: working set vs. private working set
CyberNotes: Windows Memory Usage Explained
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In this article. The working set of a process is the set of pages in the virtual address space of the process that are currently resident in physical memory.
The working set model states that a process can be in RAM if and only if all of the pages that it is currently using (often approximated by the most recently used pages) can be in RAM.
We can infer a process' working set size by observing its behavior. If a process is experiencing many page faults, its working set is larger than the memory currently allocated to it. If a process is not experiencing page faults, it may have too much memory allocated to it.
Simply said, the working set is the collection of memory pages currently owned by your process and not swapped out (i.e. in RAM). That is somewhat inaccurate, however. Reality is a lot more complicated.
Windows maintains a minimum working set size and a maximum working set size for every process. The minimum working set is easy, it is what Windows will grant to every process (as long as it can, by physical limits).
The maximum working set is more dubious. If your program uses more memory than will fit in its quota, Windows will drop some pages. However, while they are no longer in your working set, these pages are not necessarily "gone".
Rather, those pages are removed from your working set and moved to the pool of available pages. As a consequence, if some other program needs more memory and no cleared pages are left over, your pages will be cleared, and assigned to a different process. When you access them, they will need to be fetched from the swapfile again, possibly purging other pages, if you are still above the maximum working set size.
However, if nobody asked for more memory in the mean time (or if all demands could be satisfied by pages that were unused anyway), then accessing one of those pages will simply make it "magically reappear" and kick out another page in its stead.
Thus, your process can have more pages in RAM than are actually in its working set, but it does not "officially" own them.
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The Resident Set/Working Set is the portion of Virtual Address Space which is currently residing in Physical Memory and therefore isn't Swapped Out
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