From 7cbcd2e2b70d9a8547030b5a8640c85b2b7b50ab Mon Sep 17 00:00:00 2001
From: Jason Evans <jasone@canonware.com>
Date: Thu, 9 Mar 2017 18:20:02 -0800
Subject: [PATCH] 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                                          |  2 ++
 include/jemalloc/internal/jemalloc_internal_defs.h.in | 11 ++++++++---
 include/jemalloc/internal/pages_types.h               |  4 +++-
 src/pages.c                                           |  9 ++++++++-
 4 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/configure.ac b/configure.ac
index 96b105f3..db42a505 100644
--- a/configure.ac
+++ b/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], [ ])
diff --git a/include/jemalloc/internal/jemalloc_internal_defs.h.in b/include/jemalloc/internal/jemalloc_internal_defs.h.in
index 500f4274..28eb0b34 100644
--- a/include/jemalloc/internal/jemalloc_internal_defs.h.in
+++ b/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
- *                                 new pages will be demand-zeroed if the
- *                                 address region is later touched.
+ *   madvise(..., MADV_DONTNEED) : If JEMALLOC_PURGE_MADVISE_DONTNEED_ZEROS is
+ *                                 defined, this immediately discards pages,
+ *                                 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
diff --git a/include/jemalloc/internal/pages_types.h b/include/jemalloc/internal/pages_types.h
index 9e6e7c5c..e44ee2a4 100644
--- a/include/jemalloc/internal/pages_types.h
+++ b/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
 
diff --git a/src/pages.c b/src/pages.c
index 444a97c2..e80c3652 100644
--- a/src/pages.c
+++ b/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