Avoid potential issues on extent zero-out.

When custom extent_hooks or transparent huge pages are in use, the purging
semantics may change, which means we may not get zeroed pages on repopulating.
Fixing the issue by manually memset for such cases.

include/jemalloc/internal/arena_inlines_b.h

@@ -8,6 +8,11 @@
 #include "jemalloc/internal/sz.h"
 #include "jemalloc/internal/ticker.h"
 
+JEMALLOC_ALWAYS_INLINE bool
+arena_has_default_hooks(arena_t *arena) {
+	return (extent_hooks_get(arena) == &extent_hooks_default);
+}
+
 JEMALLOC_ALWAYS_INLINE arena_t *
 arena_choose_maybe_huge(tsd_t *tsd, arena_t *arena, size_t size) {
 	if (arena != NULL) {