mm/hugetlb: hugetlb_no_page: rate-limit warning message

The warning message "killed due to inadequate hugepage pool" simply
indicates that SIGBUS was sent, not that the process was forcibly killed.
If the process has a signal handler installed does not fix the problem,
this message can rapidly spam the kernel log.

On my amd64 dev machine that does not have hugepages configured, I can
reproduce the repeated warnings easily by setting vm.nr_hugepages=2 (i.e.,
4 megabytes of huge pages) and running something that sets a signal
handler and forks, like

  #include <sys/mman.h>
  #include <signal.h>
  #include <stdlib.h>
  #include <unistd.h>

  sig_atomic_t counter = 10;
  void handler(int signal)
  {
      if (counter-- == 0)
         exit(0);
  }

  int main(void)
  {
      int status;
      char *addr = mmap(NULL, 4 * 1048576, PROT_READ | PROT_WRITE,
              MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0);
      if (addr == MAP_FAILED) {perror("mmap"); return 1;}
      *addr = 'x';
      switch (fork()) {
         case -1:
            perror("fork"); return 1;
         case 0:
            signal(SIGBUS, handler);
            *addr = 'x';
            break;
         default:
            *addr = 'x';
            wait(&status);
            if (WIFSIGNALED(status)) {
               psignal(WTERMSIG(status), "child");
            }
            break;
      }
  }

Signed-off-by: Geoffrey Thomas <geofft@ldpreload.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -3502,7 +3502,7 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * COW. Warn that such a situation has occurred as it may not be obvious
 	 */
 	if (is_vma_resv_set(vma, HPAGE_RESV_UNMAPPED)) {
-		pr_warning("PID %d killed due to inadequate hugepage pool\n",
+		pr_warn_ratelimited("PID %d killed due to inadequate hugepage pool\n",
 			   current->pid);
 		return ret;
 	}