memset() is eating cpu

Issue

• The kernel needs to allocate physical memory for the executable, needing to release memory from the cache. Kernel CPU spikes here.
• Through a small program it has been observed that I/O has nothing to do with this problem. When the kernel is in the bad state memset() spikes the kernel CPU. time. The two important lines from the program are:

    void * pc = malloc(1024*1024*1024); // Allocate 1 GiB of virtual memory
    memset(pc, 1, 1024*1024*1024);      // Write the memory, which allocates physical memory

• Linux does not allocate physical pages to the process until memset() is called. That is where the kernel CPU time spikes.

Cache loaded:
    real    0m10.151s
    user    0m0.193s
    sys     0m9.936s

Cache empty:
    real    0m0.391s
    user    0m0.137s
    sys     0m0.193s