memory usage problem.

[pengkeanh]

Hi All,

I am working on optimizing the memory usage of my codes and I found a problem that I do not understand. Please let me know what you think.

Code:

typedef map <pair<string, int>, vector<pair<int, float> > > TDM;

void parsefile (TDM & my_map, string in_file); // parse input file and put it in the data map
float CheckMemUsage (void); // check memory usage by extracting /proc/self/stat info


int main (int argc, char *argv[]) {
TDM my_map;
string infile = "xxx";

printf ("INFO: Memory usage before parse file: %.2fM.\n", CheckMemUsage ());
parsefile (my_map, in_file);
printf ("INFO: Memory usage after parse file: %.2fM.\n", CheckMemUsage ());

for (TDM::iterator it=my_map.begin(); it!=my_map.end(); ++it) {
vector<pair<int, float> > ().swap (it->second);
}
TDM ().swap (my_map);
printf ("INFO: Memory usage after delete map: %.2fM.\n", CheckMemUsage ());


}

The report of this program:

INFO: Memory usage before parse file: 13.46M.
INFO: Memory usage after parse file: 203.53M.
INFO: Memory usage after delete map: 132.59M.


In the function "parsefile", I only use string, vector, pair, map stuffs, without new any memory. So after this program, I assume that only my_map is in memory. After deleting my map, the memory usage should return to before parsing file status (13.46M). But it still reports a 132.59M. What is this 132M for? Is there sth wrong in my program?

Thanks a lot for your time.

[jsmith]

Most likely you can't measure memory usage the way you are. Post the contents of CheckMemUsage.

[Athar]

It's more likely that the pages are not being released back to the OS at all when they were allocated as a result of calling new (and not by new[]), but kept around by the application for future use.
I am observing the same behavior, not only with maps.