Function cpu_allocNumaArray

quest/src/cpu/cpu_config.cpp:184–254

qcomp* cpu_allocNumaArray(qindex length) {
#if ! NUMA_AWARE
    return cpu_allocArray(length);

#elif defined(_WIN32)
    error_numaAllocOrDeallocAttemptedOnWindows();

#else
    // we will divide array's memory into pages
    long pageSize = cpu_getPageSize();
    qindex arraySize = length * sizeof(qcomp); // gauranteed no overflow

    // if entire array fits within a single page, alloc like normal
    if (arraySize <= pageSize)
        return cpu_allocArray(length);

    // otherwise we will bind pages across NUMA nodes
    static int numNodes = numa_num_configured_nodes();
    if (numNodes < 1)
        error_gettingNumNumaNodesFailed();

    qindex numPages = getNumPagesToContainArray(pageSize, arraySize);
    qindex numBytes = numPages * pageSize; // prior validation gaurantees no overflow
    
    // allocate memory, potentially more than arraySize (depending on page divisibility)
    void *rawAddr = mmap(NULL, numBytes, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
    
    // indicate memory alloc failure to caller (no NUMA-specific validation error message)
    if (rawAddr == MAP_FAILED)
        return nullptr;

    // if there is only a single NUMA node, then all memory access will occur within it
    qcomp* outAddr = reinterpret_cast<qcomp*>(rawAddr);
    if (numNodes == 1)
        return outAddr;

    // otherwise, we bind continguous pages to NUMA nodes, distributing the pages 
    // attemptedly uniformly and spreading remaining pages maximally apart
    qindex baseNumPagesPerNode = numPages / numNodes; // floors
    qindex remainingNumPagesTotal = numPages % numNodes;

    // use integer type for safe address arithmetic below
    uintptr_t offsetAddr = reinterpret_cast<uintptr_t>(rawAddr);

    for (int node=0, shift=numNodes; node < numNodes; ++node) {

        // decide number of pages to bind to NUMA node
        shift -= remainingNumPagesTotal;
        qindex numPagesInNode = baseNumPagesPerNode + (shift <= 0);
        qindex numBytesInNode = numPagesInNode * pageSize; // validation prevents overflow

        // bind those pages from the offset address to the node (identified by mask)
        unsigned long nodeMask = 1UL << node;
        unsigned long numBitsInMask = 8 * sizeof(nodeMask);
        void* nodeAddr = reinterpret_cast<void*>(offsetAddr);
        long success = mbind(nodeAddr, numBytesInNode, MPOL_BIND, &nodeMask, numBitsInMask, 0);

        // treat bind failure as internal error (even though it can result from insufficient kernel mem),