Question

How much memory or other resources is used for an individual VirtualAlloc (xxxx, yyy, MEM_RESERVE, zzz)?

Is there any difference in resource consumption (e.g. kernel paged/nonpaged pool) when I allocated one large block, like this:

VirtualAlloc( xxxx, 1024*1024, MEM_RESERVE, PAGE_READWRITE )

or multiple smaller blocks, like this:

VirtualAlloc( xxxx, 64*1024, MEM_RESERVE, PAGE_READWRITE );
VirtualAlloc( xxxx+1*64*1024, 64*1024, MEM_RESERVE, PAGE_READWRITE );
VirtualAlloc( xxxx+2*64*1024, 64*1024, MEM_RESERVE, PAGE_READWRITE );
...
VirtualAlloc( xxxx+15*64*1024, 64*1024, MEM_RESERVE, PAGE_READWRITE );

If someone does not know the answer but can suggest an experiment which would be able to check it, it will be helpful as well.

The motivation is I want to implement returning memory back to OS for TCMalloc under Windows. My idea is to replace individual large VirtualAlloc calls by performing a sequence of small (allocation granularity) calls, so that I can call VirtualFree on each of them. I am aware this way the allocation of large blocks will be slower, but are there any resource consumption penalties be expected?

Answer 1

Just FYI, you can use GetProcessMemoryInfo and GlobalMemoryStatusEx to get some memory usage measurements.

void DisplayMemoryUsageInformation()
{
    HANDLE hProcess = GetCurrentProcess();
    PROCESS_MEMORY_COUNTERS pmc;
    ZeroMemory(&pmc,sizeof(pmc));
    GetProcessMemoryInfo(hProcess,&pmc, sizeof(pmc));
    std::cout << "PageFaultCount:             " << pmc.PageFaultCount             << std::endl;
    std::cout << "PeakWorkingSetSize:         " << pmc.PeakWorkingSetSize         << std::endl;
    std::cout << "WorkingSetSize:             " << pmc.WorkingSetSize             << std::endl;
    std::cout << "QuotaPeakPagedPoolUsage:    " << pmc.QuotaPeakPagedPoolUsage    << std::endl;
    std::cout << "QuotaPagedPoolUsage:        " << pmc.QuotaPagedPoolUsage        << std::endl;
    std::cout << "QuotaPeakNonPagedPoolUsage: " << pmc.QuotaPeakNonPagedPoolUsage << std::endl;
    std::cout << "QuotaNonPagedPoolUsage:     " << pmc.QuotaNonPagedPoolUsage     << std::endl;
    std::cout << "PagefileUsage:              " << pmc.PagefileUsage              << std::endl;
    std::cout << "PeakPagefileUsage:          " << pmc.PeakPagefileUsage          << std::endl;

    MEMORYSTATUSEX msx;
    ZeroMemory(&msx,sizeof(msx));
    msx.dwLength = sizeof(msx);
    GlobalMemoryStatusEx(&msx);
    std::cout << "MemoryLoad:                 " << msx.dwMemoryLoad               << std::endl;
    std::cout << "TotalPhys:                  " << msx.ullTotalPhys               << std::endl;
    std::cout << "AvailPhys:                  " << msx.ullAvailPhys               << std::endl;
    std::cout << "TotalPageFile:              " << msx.ullTotalPageFile           << std::endl;
    std::cout << "AvailPageFile:              " << msx.ullAvailPageFile           << std::endl;
    std::cout << "TotalVirtual:               " << msx.ullTotalVirtual            << std::endl;
    std::cout << "AvailVirtual:               " << msx.ullAvailVirtual            << std::endl;
    std::cout << "AvailExtendedVirtual:       " << msx.ullAvailExtendedVirtual    << std::endl;
}