Fix pages_purge_forced() to discard pages on non-Linux systems.

madvise(..., MADV_DONTNEED) only causes demand-zeroing on Linux, so fall
back to overlaying a new mapping.

configure.ac

@@ -547,6 +547,7 @@ case "${host}" in
 	dnl syscall(2) and secure_getenv(3) are exposed by _GNU_SOURCE.
 	JE_APPEND_VS(CPPFLAGS, -D_GNU_SOURCE)
 	abi="elf"
+	AC_DEFINE([JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS])
 	AC_DEFINE([JEMALLOC_HAS_ALLOCA_H])
 	AC_DEFINE([JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY], [ ])
 	AC_DEFINE([JEMALLOC_THREADED_INIT], [ ])
@@ -558,6 +559,7 @@ case "${host}" in
 	dnl syscall(2) and secure_getenv(3) are exposed by _GNU_SOURCE.
 	JE_APPEND_VS(CPPFLAGS, -D_GNU_SOURCE)
 	abi="elf"
+	AC_DEFINE([JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS])
 	AC_DEFINE([JEMALLOC_HAS_ALLOCA_H])
 	AC_DEFINE([JEMALLOC_PROC_SYS_VM_OVERCOMMIT_MEMORY], [ ])
 	AC_DEFINE([JEMALLOC_THREADED_INIT], [ ])

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -265,12 +265,17 @@
  *
  *   madvise(..., MADV_FREE) : This marks pages as being unused, such that they
  *                             will be discarded rather than swapped out.
- *   madvise(..., MADV_DONTNEED) : This immediately discards pages, such that
+ *   madvise(..., MADV_DONTNEED) : If JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS is
- *                                 new pages will be demand-zeroed if the
+ *                                 defined, this immediately discards pages,
- *                                 address region is later touched.
+ *                                 such that new pages will be demand-zeroed if
+ *                                 the address region is later touched;
+ *                                 otherwise this behaves similarly to
+ *                                 MADV_FREE, though typically with higher
+ *                                 system overhead.
  */
 #undef JEMALLOC_PURGE_MADVISE_FREE
 #undef JEMALLOC_PURGE_MADVISE_DONTNEED
+#undef JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS
 
 /*
  * Defined if transparent huge pages are supported via the MADV_[NO]HUGEPAGE

include/jemalloc/internal/pages_types.h

@@ -37,7 +37,9 @@
  * next step after purging on Windows anyway, there's no point in adding such
  * complexity.
  */
-#if !defined(_WIN32) && defined(JEMALLOC_PURGE_MADVISE_DONTNEED)
+#if !defined(_WIN32) && ((defined(JEMALLOC_PURGE_MADVISE_DONTNEED) && \
+    defined(JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS)) || \
+    defined(JEMALLOC_MAPS_COALESCE))
 #  define PAGES_CAN_PURGE_FORCED
 #endif
 

src/pages.c

@@ -170,6 +170,9 @@ pages_purge_lazy(void *addr, size_t size) {
 	VirtualAlloc(addr, size, MEM_RESET, PAGE_READWRITE);
 #elif defined(JEMALLOC_PURGE_MADVISE_FREE)
 	madvise(addr, size, MADV_FREE);
+#elif defined(JEMALLOC_PURGE_MADVISE_DONTNEED) && \
+    !defined(JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS)
+	madvise(addr, size, MADV_DONTNEED);
 #else
 	not_reached();
 #endif
@@ -182,8 +185,12 @@ pages_purge_forced(void *addr, size_t size) {
 		return true;
 	}
 
-#if defined(JEMALLOC_PURGE_MADVISE_DONTNEED)
+#if defined(JEMALLOC_PURGE_MADVISE_DONTNEED) && \
+    defined(JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS)
 	return (madvise(addr, size, MADV_DONTNEED) != 0);
+#elif defined(JEMALLOC_MAPS_COALESCE)
+	/* Try to overlay a new demand-zeroed mapping. */
+	return pages_commit(addr, size);
 #else
 	not_reached();
 #endif