Why does the system call clear_huge_page still occur?

My OS is CentOS 7 latest. I set the isolcpus and transparent_hugepage=never default_hugepagesz=1G hugepagesz=1G in the cmdline to isolate cpus and enable huge pages with 1G per page. And I move all the irqs that can be binded to specified CPU cores.

My init function for using huge pages

bool initSharedMemory(const char* nm, std::size_t bytes){
    int tid = ftok(nm, 'R');
    if (tid == -1) {
        fprintf(stderr, "ftok error: %d - %s\n", tid, strerror(-tid));
        return false;
    }
    mSHMID = shmget(tid, bytes, SHM_HUGETLB | IPC_CREAT | SHM_R | SHM_W);
    if (mSHMID < 0) {
        fprintf(stderr, "shmget error: %d - %s\n", mSHMID, strerror(-mSHMID));
        return false;
    }
    mMemory = (uint8_t*)shmat(mSHMID, nullptr, 0);
    if (mMemory == (uint8_t*)(-1)) {
        fprintf(stderr, "shmat error\n");
        return false;
    }
    mSize = bytes;
    return true;
}

I run my program with taskset and perf record. I find that there are some kallsyms about huge page clear,

 99.73%  test_stx2  test_stx2             [.] Stx::run                                                                [.] Stx::run                                                                -
 0.03%  test_stx2  [kernel.kallsyms]     [k] clear_page                                                              [k] clear_page_c_e                                                          -
 0.03%  test_stx2  [kernel.kallsyms]     [k] clear_huge_page                                                         [k] _cond_resched                                                           -
 0.03%  test_stx2  [kernel.kallsyms]     [k] _cond_resched                                                           [k] clear_huge_page                                                         -
 0.03%  test_stx2  [kernel.kallsyms]     [k] clear_huge_page                                                         [k] clear_page                                                              -
 0.02%  test_stx2  [kernel.kallsyms]     [k] clear_page_c_e                                                          [k] clear_huge_page                                                         -
 0.02%  test_stx2  [kernel.kallsyms]     [k] clear_huge_page                                                         [k] clear_huge_page                                                         -
 0.02%  test_stx2  test_stx2             [.] std::__fill_n_a<unsigned long*, unsigned long, unsigned long>           [.] std::__fill_n_a<unsigned long*, unsigned long, unsigned long>           -
 0.00%  test_stx2  [kernel.kallsyms]     [.] retint_userspace_restore_args                                           [.] retint_userspace_restore_args                                           -
 0.00%  test_stx2  [kernel.kallsyms]     [k] task_tick_fair                                                          [k] task_tick_fair                                                          -
 0.00%  test_stx2  [kernel.kallsyms]     [k] irq_exit                                                                [k] irq_exit                                                                -
 0.00%  test_stx2  [kernel.kallsyms]     [k] zone_statistics                                                         [k] zone_statistics                                                         -
 0.00%  test_stx2  [kernel.kallsyms]     [k] do_softirq                                                              [k] do_softirq                                                              -
 0.00%  test_stx2  [kernel.kallsyms]     [k] __update_cpu_load                                                       [k] __update_cpu_load                                                       -
 0.00%  test_stx2  [kernel.kallsyms]     [k] scheduler_tick                                                          [k] scheduler_tick                                                          -
 0.00%  test_stx2  [kernel.kallsyms]     [k] trigger_load_balance                                                    [k] trigger_load_balance                                                    -
 0.00%  test_stx2  [kernel.kallsyms]     [k] __hrtimer_run_queues                                                    [k] __hrtimer_run_queues                                                    -
 0.00%  test_stx2  [kernel.kallsyms]     [k] run_posix_cpu_timers                                                    [k] run_posix_cpu_timers                                                    -
 0.00%  test_stx2  [kernel.kallsyms]     [k] zone_statistics                                                         [k] __inc_zone_state                                                        -
 0.00%  test_stx2  [kernel.kallsyms]     [.] retint_userspace_restore_args                                           [.] irq_return                                                              -
 0.00%  test_stx2  [kernel.kallsyms]     [k] __inc_zone_state                                                        [k] zone_statistics                                                         -
 0.00%  test_stx2  [kernel.kallsyms]     [.] handle_mm_fault                                                         [.] handle_mm_fault                                                         -
 0.00%  test_stx2  [kernel.kallsyms]     [.] __do_page_fault                                                         [.] __do_page_fault                                                         -
 0.00%  test_stx2  [kernel.kallsyms]     [k] __x86_indirect_thunk_rax                                                [k] read_tsc                  

I cannot understand that why there are some clear_page operation. -