Implement opt.metadata_thp

This option enables transparent huge page for base allocators (require
MADV_HUGEPAGE support).

include/jemalloc/internal/base_externs.h

@@ -1,6 +1,8 @@
 #ifndef JEMALLOC_INTERNAL_BASE_EXTERNS_H
 #define JEMALLOC_INTERNAL_BASE_EXTERNS_H
 
+extern bool opt_metadata_thp;
+
 base_t *b0get(void);
 base_t *base_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks);
 void base_delete(tsdn_t *tsdn, base_t *base);

include/jemalloc/internal/base_types.h

@@ -4,4 +4,6 @@
 typedef struct base_block_s base_block_t;
 typedef struct base_s base_t;
 
+#define METADATA_THP_DEFAULT false
+
 #endif /* JEMALLOC_INTERNAL_BASE_TYPES_H */

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -260,6 +260,12 @@
 /* Defined if madvise(2) is available. */
 #undef JEMALLOC_HAVE_MADVISE
 
+/*
+ * Defined if transparent huge pages are supported via the MADV_[NO]HUGEPAGE
+ * arguments to madvise(2).
+ */
+#undef JEMALLOC_HAVE_MADVISE_HUGE
+
 /*
  * Methods for purging unused pages differ between operating systems.
  *

include/jemalloc/internal/pages.h

@@ -58,6 +58,9 @@ static const bool pages_can_purge_forced =
 #endif
     ;
 
+/* Whether transparent huge page state is "madvise". */
+extern bool thp_state_madvise;
+
 void *pages_map(void *addr, size_t size, size_t alignment, bool *commit);
 void pages_unmap(void *addr, size_t size);
 bool pages_commit(void *addr, size_t size);