Function os_overcommits_proc

app/redis-6.2.6/deps/jemalloc/src/pages.c:435–493

* Use syscall(2) rather than {open,read,close}(2) when possible to avoid * reentry during bootstrapping if another library has interposed system call * wrappers. */

 * wrappers.
 */
static bool
os_overcommits_proc(void) {
	int fd;
	char buf[1];

#if defined(JEMALLOC_USE_SYSCALL) && defined(SYS_open)
	#if defined(O_CLOEXEC)
		fd = (int)syscall(SYS_open, "/proc/sys/vm/overcommit_memory", O_RDONLY |
			O_CLOEXEC);
	#else
		fd = (int)syscall(SYS_open, "/proc/sys/vm/overcommit_memory", O_RDONLY);
		if (fd != -1) {
			fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
		}
	#endif
#elif defined(JEMALLOC_USE_SYSCALL) && defined(SYS_openat)
	#if defined(O_CLOEXEC)
		fd = (int)syscall(SYS_openat,
			AT_FDCWD, "/proc/sys/vm/overcommit_memory", O_RDONLY | O_CLOEXEC);
	#else
		fd = (int)syscall(SYS_openat,
			AT_FDCWD, "/proc/sys/vm/overcommit_memory", O_RDONLY);
		if (fd != -1) {
			fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
		}
	#endif
#else
	#if defined(O_CLOEXEC)
		fd = open("/proc/sys/vm/overcommit_memory", O_RDONLY | O_CLOEXEC);
	#else
		fd = open("/proc/sys/vm/overcommit_memory", O_RDONLY);
		if (fd != -1) {
			fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
		}
	#endif
#endif

	if (fd == -1) {
		return false; /* Error. */
	}

	ssize_t nread = malloc_read_fd(fd, &buf, sizeof(buf));
#if defined(JEMALLOC_USE_SYSCALL) && defined(SYS_close)
	syscall(SYS_close, fd);
#else
	close(fd);
#endif

	if (nread < 1) {
		return false; /* Error. */
	}
	/*
	 * /proc/sys/vm/overcommit_memory meanings:
	 * 0: Heuristic overcommit.
	 * 1: Always overcommit.
	 * 2: Never overcommit.
	 */
	return (buf[0] == '0' || buf[0] == '1');