Zend,fibers: Ensure fiber stack is not backed by THP.

Ending with fiber stack mapped in hugepages will affect performance
badly.
Until < Linux 6.8-rc2 MAP_STACK was a noop, now it implies no THP, older releases
need MAP_GROWSDOWN to signal it is a stack like segment and therefore no THP.

Author: crrodriguez

Zend/zend_fibers.c

@@ -56,6 +56,10 @@
 #  define MAP_STACK 0
 # endif
 
+#if !defined(MAP_GROWSDOWN)
+#define MAP_GROWSDOWN 0
+#endif
+
 # ifndef MAP_FAILED
 #  define MAP_FAILED ((void * ) -1)
 # endif
@@ -237,7 +241,7 @@ static zend_fiber_stack *zend_fiber_stack_allocate(size_t size)
 	}
 # endif
 #else
-	pointer = mmap(NULL, alloc_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+	pointer = mmap(NULL, alloc_size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK | MAP_GROWSDOWN, -1, 0);
 
 	if (pointer == MAP_FAILED) {
 		zend_throw_exception_ex(NULL, 0, "Fiber stack allocate failed: mmap failed: %s (%d)", strerror(errno), errno);