Mark partially purged arena chunks as non-hugepage.

Add the pages_[no]huge() functions, which toggle huge page state via
madvise(..., MADV_[NO]HUGEPAGE) calls.

The first time a page run is purged from within an arena chunk, call
pages_nohuge() to tell the kernel to make no further attempts to back
the chunk with huge pages.  Upon arena chunk deletion, restore the
associated virtual memory to its original state via pages_huge().

This resolves #243.

include/jemalloc/internal/arena.h

@@ -190,6 +190,14 @@ struct arena_chunk_s {
 	 */
 	extent_node_t		node;
 
+	/*
+	 * True if memory could be backed by transparent huge pages.  This is
+	 * only directly relevant to Linux, since it is the only supported
+	 * platform on which jemalloc interacts with explicit transparent huge
+	 * page controls.
+	 */
+	bool			hugepage;
+
 	/*
 	 * Map of pages within chunk that keeps track of free/large/small.  The
 	 * first map_bias entries are omitted, since the chunk header does not

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -265,6 +265,12 @@
 #undef JEMALLOC_PURGE_MADVISE_FREE
 #undef JEMALLOC_PURGE_MADVISE_DONTNEED
 
+/*
+ * Defined if transparent huge pages are supported via the MADV_[NO]HUGEPAGE
+ * arguments to madvise(2).
+ */
+#undef JEMALLOC_THP
+
 /* Define if operating system has alloca.h header. */
 #undef JEMALLOC_HAS_ALLOCA_H
 

include/jemalloc/internal/pages.h

@@ -16,6 +16,8 @@ void	*pages_trim(void *addr, size_t alloc_size, size_t leadsize,
 bool	pages_commit(void *addr, size_t size);
 bool	pages_decommit(void *addr, size_t size);
 bool	pages_purge(void *addr, size_t size);
+bool	pages_huge(void *addr, size_t size);
+bool	pages_nohuge(void *addr, size_t size);
 void	pages_boot(void);
 
 #endif /* JEMALLOC_H_EXTERNS */

include/jemalloc/internal/private_symbols.txt

@@ -397,7 +397,9 @@ p2rz
 pages_boot
 pages_commit
 pages_decommit
+pages_huge
 pages_map
+pages_nohuge
 pages_purge
 pages_trim
 pages_unmap