Memory usage bug...

[Nick Z.]

When I profile my application the profiler tells me that there is
roughly 4MB of memory used throughout the lifetime, which seems reasonable.

However, when I start the task manager the said memory usage is 20MB
right after starting the program and 80MB after running it. However, if
you start the program and keep the task manager open to monitor usage,
it says 20MB, however, when you minimize the program, the memory usage
falls to 2MB.

This is a known bug as far as I know
see:
http://groups.google.com/group/micr...memory+usage+c#&rnum=5&hl=en#cf6554802f9f3728
(watch for wrap)

However, I want to know if the memory is really being held back from the
OS until you minimize the application or is there some other explanation?

Thanks,
Nick Z.

 

[Guest]

When I profile my application the profiler tells me that there is

roughly 4MB of memory used throughout the lifetime, which seems reasonable.
However, when I start the task manager the said memory usage is 20MB
right after starting the program and 80MB after running it. However, if
you start the program and keep the task manager open to monitor usage,
it says 20MB, however, when you minimize the program, the memory usage
falls to 2MB.

The figure that is ballooning up and down (2mb-80mb from task manager) is the
working set size, not the amount of memory currently in use (4mb from
profiler).

This is a known bug as far as I know

The behaviour is not a bug, it is by design.

However, I want to know if the memory is really being held back from the
OS until you minimize the application or is there some other explanation?

The memory is not "being held back" from the OS. In the presence of ample
physical memory, the OS does not enforce the process's working set
maximum size. So, we have poor nomenclature, but not a bug. When an
app is minimized, the OS calls Win32 API SetProcessWorkingSetSize to
minimize the working set size, and that is why the task manager reports
the big drop.

FYI, the app can call the API as well, and I have done so while chasing a
memory leak regarding failure to release unmanaged resources. So, there
is at least one development context where MS memory management is an
inconvenience. You and many others have inquired about this issue, so
there is massive confusion and concern about it. I don't know why MS did what
they did. My guess is that there is an advantage to deferring the reclamation
of memory pages - perhaps leaving pages in limbo (reclaimable but still
assigned
to a process) expidites subsequent memory allocations by the same process.

 

[Nick Z.]

Thanks for the feedback. However, I'm still not quite sure how this
affects performance. Lets say the OS needs some memory, and there is
not enough of it, will the OS invoke the SetProcessWorkingSetSize on
every process untill it get enough memory or will it look at the
working set and asume that all of it is required for the process to
function?

 

[Willy Denoyette [MVP]]

Thanks for the feedback. However, I'm still not quite sure how this
affects performance. Lets say the OS needs some memory, and there is
not enough of it, will the OS invoke the SetProcessWorkingSetSize on
every process untill it get enough memory or will it look at the
working set and asume that all of it is required for the process to
function?

No, the OS never calls SetProcessWorkingSetSize, this is a user API. The
memory manager will free RAM space by removing the least frequently used
pages from the processes working sets until there is enough free space to
accomodate the memory request. Note that this is done long before memory is
exhausted, the memory manager and the balance-set manager run once per
second.
I would suggest you read this
http://emea.windowsitpro.com/Article/ArticleID/3686/3686.html if you like to
know how the OS manages it's memory.

Willy.

 

[Mehdi]

When I profile my application the profiler tells me that there is
roughly 4MB of memory used throughout the lifetime, which seems reasonable.

However, when I start the task manager the said memory usage is 20MB
right after starting the program and 80MB after running it. However, if
you start the program and keep the task manager open to monitor usage,
it says 20MB, however, when you minimize the program, the memory usage
falls to 2MB.

This article explains quite clearly the reasons for this behaviour:
http://getdotnetco.web101.discountasp.net/GdncStore/free/Articles/The Memory Mystery.htm
("The Memory Mystery" by Michael McIntyre)

 

[Nick Z.]

Thank you very much for the link, that explained it.
I thought something similar was happening, I just didn't know exactly
what was happening and how to explain it.

Thanks,
Nick Z.