Refactor purging and splitting/merging.

Split purging into lazy and forced variants.  Use the forced variant for
zeroing dss.

Add support for NULL function pointers as an opt-out mechanism for the
dalloc, commit, decommit, purge_lazy, purge_forced, split, and merge
fields of extent_hooks_t.

Add short-circuiting checks in large_ralloc_no_move_{shrink,expand}() so
that no attempt is made if splitting/merging is not supported.

This resolves #268.

1 files changed, 34 insertions, 1 deletions

diff --git a/include/jemalloc/internal/pages.h b/include/jemalloc/internal/pages.h
index 034a8aa..98e4f38 100644
--- a/include/jemalloc/internal/pages.h
+++ b/include/jemalloc/internal/pages.h
@@ -24,6 +24,23 @@
 #define	HUGEPAGE_CEILING(s)						\
 	(((s) + HUGEPAGE_MASK) & ~HUGEPAGE_MASK)
 
+/* PAGES_CAN_PURGE_LAZY is defined if lazy purging is supported. */
+#if defined(_WIN32) || defined(JEMALLOC_PURGE_MADVISE_FREE)
+#  define PAGES_CAN_PURGE_LAZY
+#endif
+/*
+ * PAGES_CAN_PURGE_FORCED is defined if forced purging is supported.
+ *
+ * The only supported way to hard-purge on Windows is to decommit and then
+ * re-commit, but doing so is racy, and if re-commit fails it's a pain to
+ * propagate the "poisoned" memory state.  Since we typically decommit as the
+ * next step after purging on Windows anyway, there's no point in adding such
+ * complexity.
+ */
+#if !defined(_WIN32) && defined(JEMALLOC_PURGE_MADVISE_DONTNEED)
+#  define PAGES_CAN_PURGE_FORCED
+#endif
+
 #endif /* JEMALLOC_H_TYPES */
 /******************************************************************************/
 #ifdef JEMALLOC_H_STRUCTS
@@ -32,13 +49,29 @@
 /******************************************************************************/
 #ifdef JEMALLOC_H_EXTERNS
 
+static const bool pages_can_purge_lazy =
+#ifdef PAGES_CAN_PURGE_LAZY
+    true
+#else
+    false
+#endif
+    ;
+static const bool pages_can_purge_forced =
+#ifdef PAGES_CAN_PURGE_FORCED
+    true
+#else
+    false
+#endif
+    ;
+
 void	*pages_map(void *addr, size_t size, bool *commit);
 void	pages_unmap(void *addr, size_t size);
 void	*pages_trim(void *addr, size_t alloc_size, size_t leadsize,
     size_t size, bool *commit);
 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_purge_lazy(void *addr, size_t size);
+bool	pages_purge_forced(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);