add experimental.arenas_create_ext mallctl

This mallctl accepts an arena_config_t structure which
can be used to customize the behavior of the arena.
Right now it contains extent_hooks and a new option,
metadata_use_hooks, which controls whether the extent
hooks are also used for metadata allocation.

The medata_use_hooks option has two main use cases:

1. In heterogeneous memory systems, to avoid metadata
being placed on potentially slower memory.

2. Avoiding virtual memory from being leaked as a result
of metadata allocation failure originating in an extent hook.

include/jemalloc/internal/arena_externs.h

@@ -97,7 +97,7 @@ bool arena_retain_grow_limit_get_set(tsd_t *tsd, arena_t *arena,
 unsigned arena_nthreads_get(arena_t *arena, bool internal);
 void arena_nthreads_inc(arena_t *arena, bool internal);
 void arena_nthreads_dec(arena_t *arena, bool internal);
-arena_t *arena_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks);
+arena_t *arena_new(tsdn_t *tsdn, unsigned ind, const arena_config_t *config);
 bool arena_init_huge(void);
 bool arena_is_huge(unsigned arena_ind);
 arena_t *arena_choose_huge(tsd_t *tsd);

include/jemalloc/internal/arena_types.h

@@ -41,4 +41,18 @@ typedef enum {
  */
 #define OVERSIZE_THRESHOLD_DEFAULT (8 << 20)
 
+struct arena_config_s {
+	/* extent hooks to be used for the arena */
+	struct extent_hooks_s *extent_hooks;
+
+	/*
+	 * Use extent hooks for metadata (base) allocations when true.
+	 */
+	bool metadata_use_hooks;
+};
+
+typedef struct arena_config_s arena_config_t;
+
+extern const arena_config_t arena_config_default;
+
 #endif /* JEMALLOC_INTERNAL_ARENA_TYPES_H */

include/jemalloc/internal/base.h

@@ -46,6 +46,11 @@ struct base_s {
 	 */
 	ehooks_t ehooks;
 
+	/*
+	 * Use user hooks for metadata when true.
+	 */
+	bool metadata_use_hooks;
+
 	/* Protects base_alloc() and base_stats_get() operations. */
 	malloc_mutex_t mtx;
 
@@ -87,7 +92,7 @@ metadata_thp_enabled(void) {
 
 base_t *b0get(void);
 base_t *base_new(tsdn_t *tsdn, unsigned ind,
-    const extent_hooks_t *extent_hooks);
+    const extent_hooks_t *extent_hooks, bool metadata_use_hooks);
 void base_delete(tsdn_t *tsdn, base_t *base);
 ehooks_t *base_ehooks_get(base_t *base);
 extent_hooks_t *base_extent_hooks_set(base_t *base,

include/jemalloc/internal/base_structs.h

@@ -25,6 +25,11 @@ struct base_s {
 	 */
 	ehooks_t ehooks;
 
+	/*
+	 * Use user hooks for metadata when true.
+	 */
+	bool metadata_use_hooks;
+
 	/* Protects base_alloc() and base_stats_get() operations. */
 	malloc_mutex_t mtx;
 

include/jemalloc/internal/jemalloc_internal_externs.h

@@ -57,7 +57,7 @@ void *bootstrap_calloc(size_t num, size_t size);
 void bootstrap_free(void *ptr);
 void arena_set(unsigned ind, arena_t *arena);
 unsigned narenas_total_get(void);
-arena_t *arena_init(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks);
+arena_t *arena_init(tsdn_t *tsdn, unsigned ind, const arena_config_t *config);
 arena_t *arena_choose_hard(tsd_t *tsd, bool internal);
 void arena_migrate(tsd_t *tsd, unsigned oldind, unsigned newind);
 void iarena_cleanup(tsd_t *tsd);

include/jemalloc/internal/jemalloc_internal_inlines_a.h

@@ -66,7 +66,7 @@ arena_get(tsdn_t *tsdn, unsigned ind, bool init_if_missing) {
 	if (unlikely(ret == NULL)) {
 		if (init_if_missing) {
 			ret = arena_init(tsdn, ind,
-			    (extent_hooks_t *)&ehooks_default_extent_hooks);
+			    &arena_config_default);
 		}
 	}
 	return ret;