--- a/src/hotspot/share/gc/z/zFuture.hpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zFuture.hpp	Mon Oct 28 11:27:27 2019 +0100
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -34,7 +34,10 @@
   T         _value;
 
 public:
+  ZFuture();
+
   void set(T value);
+  T peek();
   T get();
 };
 

--- a/src/hotspot/share/gc/z/zFuture.inline.hpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zFuture.inline.hpp	Mon Oct 28 11:27:27 2019 +0100
@@ -29,6 +29,10 @@
 #include "runtime/thread.hpp"
 
 template <typename T>
+inline ZFuture<T>::ZFuture() :
+    _value() {}
+
+template <typename T>
 inline void ZFuture<T>::set(T value) {
   // Set value
   _value = value;
@@ -38,6 +42,11 @@
 }
 
 template <typename T>
+inline T ZFuture<T>::peek() {
+  return _value;
+}
+
+template <typename T>
 inline T ZFuture<T>::get() {
   // Wait for notification
   Thread* const thread = Thread::current();

--- a/src/hotspot/share/gc/z/zHeap.cpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zHeap.cpp	Mon Oct 28 11:27:27 2019 +0100
@@ -244,34 +244,14 @@
   return _page_allocator.uncommit(delay);
 }
 
-void ZHeap::before_flip() {
-  if (ZVerifyViews) {
-    // Unmap all pages
-    _page_allocator.debug_unmap_all_pages();
-  }
-}
-
-void ZHeap::after_flip() {
-  if (ZVerifyViews) {
-    // Map all pages
-    ZPageTableIterator iter(&_page_table);
-    for (ZPage* page; iter.next(&page);) {
-      _page_allocator.debug_map_page(page);
-    }
-    _page_allocator.debug_map_cached_pages();
-  }
-}
-
 void ZHeap::flip_to_marked() {
-  before_flip();
+  ZVerifyViewsFlip flip(&_page_allocator);
   ZAddress::flip_to_marked();
-  after_flip();
 }
 
 void ZHeap::flip_to_remapped() {
-  before_flip();
+  ZVerifyViewsFlip flip(&_page_allocator);
   ZAddress::flip_to_remapped();
-  after_flip();
 }
 
 void ZHeap::mark_start() {
@@ -460,6 +440,14 @@
   iter.objects_do(cl, visit_weaks);
 }
 
+void ZHeap::pages_do(ZPageClosure* cl) {
+  ZPageTableIterator iter(&_page_table);
+  for (ZPage* page; iter.next(&page);) {
+    cl->do_page(page);
+  }
+  _page_allocator.pages_do(cl);
+}
+
 void ZHeap::serviceability_initialize() {
   _serviceability.initialize();
 }

--- a/src/hotspot/share/gc/z/zHeap.hpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zHeap.hpp	Mon Oct 28 11:27:27 2019 +0100
@@ -63,9 +63,6 @@
   size_t heap_max_size() const;
   size_t heap_max_reserve_size() const;
 
-  void before_flip();
-  void after_flip();
-
   void flip_to_marked();
   void flip_to_remapped();
 
@@ -151,6 +148,7 @@
 
   // Iteration
   void object_iterate(ObjectClosure* cl, bool visit_weaks);
+  void pages_do(ZPageClosure* cl);
 
   // Serviceability
   void serviceability_initialize();

--- a/src/hotspot/share/gc/z/zPage.hpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zPage.hpp	Mon Oct 28 11:27:27 2019 +0100
@@ -112,4 +112,9 @@
   void print() const;
 };
 
+class ZPageClosure {
+public:
+  virtual void do_page(const ZPage* page) = 0;
+};
+
 #endif // SHARE_GC_Z_ZPAGE_HPP

--- a/src/hotspot/share/gc/z/zPageAllocator.cpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zPageAllocator.cpp	Mon Oct 28 11:27:27 2019 +0100
@@ -60,7 +60,9 @@
       _type(type),
       _size(size),
       _flags(flags),
-      _total_collections(total_collections) {}
+      _total_collections(total_collections),
+      _node(),
+      _result() {}
 
   uint8_t type() const {
     return _type;
@@ -78,6 +80,10 @@
     return _total_collections;
   }
 
+  ZPage* peek() {
+    return _result.peek();
+  }
+
   ZPage* wait() {
     return _result.get();
   }
@@ -108,6 +114,7 @@
     _allocated(0),
     _reclaimed(0),
     _queue(),
+    _satisfied(),
     _safe_delete(),
     _uncommit(false),
     _initialized(false) {
@@ -289,11 +296,7 @@
 
 void ZPageAllocator::map_page(const ZPage* page) const {
   // Map physical memory
-  if (!page->is_mapped()) {
-    _physical.map(page->physical_memory(), page->start());
-  } else if (ZVerifyViews) {
-    _physical.debug_map(page->physical_memory(), page->start());
-  }
+  _physical.map(page->physical_memory(), page->start());
 }
 
 size_t ZPageAllocator::max_available(bool no_reserve) const {
@@ -433,14 +436,21 @@
     } while (page == gc_marker);
 
     {
-      // Guard deletion of underlying semaphore. This is a workaround for a
-      // bug in sem_post() in glibc < 2.21, where it's not safe to destroy
+      //
+      // We grab the lock here for two different reasons:
+      //
+      // 1) Guard deletion of underlying semaphore. This is a workaround for
+      // a bug in sem_post() in glibc < 2.21, where it's not safe to destroy
       // the semaphore immediately after returning from sem_wait(). The
       // reason is that sem_post() can touch the semaphore after a waiting
       // thread have returned from sem_wait(). To avoid this race we are
       // forcing the waiting thread to acquire/release the lock held by the
       // posting thread. https://sourceware.org/bugzilla/show_bug.cgi?id=12674
+      //
+      // 2) Guard the list of satisfied pages.
+      //
       ZLocker<ZLock> locker(&_lock);
+      _satisfied.remove(&request);
     }
   }
 
@@ -462,7 +472,9 @@
   }
 
   // Map page if needed
-  map_page(page);
+  if (!page->is_mapped()) {
+    map_page(page);
+  }
 
   // Reset page. This updates the page's sequence number and must
   // be done after page allocation, which potentially blocked in
@@ -500,6 +512,7 @@
     // the dequeue operation must happen first, since the request
     // will immediately be deallocated once it has been satisfied.
     _queue.remove(request);
+    _satisfied.insert_first(request);
     request->satisfy(page);
   }
 }
@@ -686,28 +699,21 @@
   _physical.debug_map(page->physical_memory(), page->start());
 }
 
-class ZPageCacheDebugMapClosure : public StackObj {
-private:
-  const ZPageAllocator* const _allocator;
-
-public:
-  ZPageCacheDebugMapClosure(const ZPageAllocator* allocator) :
-      _allocator(allocator) {}
-
-  virtual void do_page(const ZPage* page) {
-    _allocator->debug_map_page(page);
-  }
-};
-
-void ZPageAllocator::debug_map_cached_pages() const {
+void ZPageAllocator::debug_unmap_page(const ZPage* page) const {
   assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
-  ZPageCacheDebugMapClosure cl(this);
-  _cache.pages_do(&cl);
+  _physical.debug_unmap(page->physical_memory(), page->start());
 }
 
-void ZPageAllocator::debug_unmap_all_pages() const {
-  assert(SafepointSynchronize::is_at_safepoint(), "Should be at safepoint");
-  _physical.debug_unmap(ZPhysicalMemorySegment(0 /* start */, ZAddressOffsetMax), 0 /* offset */);
+void ZPageAllocator::pages_do(ZPageClosure* cl) const {
+  ZListIterator<ZPageAllocRequest> iter(&_satisfied);
+  for (ZPageAllocRequest* request; iter.next(&request);) {
+    const ZPage* const page = request->peek();
+    if (page != NULL) {
+      cl->do_page(page);
+    }
+  }
+
+  _cache.pages_do(cl);
 }
 
 bool ZPageAllocator::is_alloc_stalled() const {
@@ -728,7 +734,8 @@
     }
 
     // Out of memory, fail allocation request
-    _queue.remove_first();
+    _queue.remove(request);
+    _satisfied.insert_first(request);
     request->satisfy(NULL);
   }
 }

--- a/src/hotspot/share/gc/z/zPageAllocator.hpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zPageAllocator.hpp	Mon Oct 28 11:27:27 2019 +0100
@@ -54,11 +54,12 @@
   size_t                     _allocated;
   ssize_t                    _reclaimed;
   ZList<ZPageAllocRequest>   _queue;
+  ZList<ZPageAllocRequest>   _satisfied;
   mutable ZSafeDelete<ZPage> _safe_delete;
   bool                       _uncommit;
   bool                       _initialized;
 
-  static ZPage* const      gc_marker;
+  static ZPage* const gc_marker;
 
   void prime_cache(size_t size);
 
@@ -117,11 +118,12 @@
   void map_page(const ZPage* page) const;
 
   void debug_map_page(const ZPage* page) const;
-  void debug_map_cached_pages() const;
-  void debug_unmap_all_pages() const;
+  void debug_unmap_page(const ZPage* page) const;
 
   bool is_alloc_stalled() const;
   void check_out_of_memory();
+
+  void pages_do(ZPageClosure* cl) const;
 };
 
 #endif // SHARE_GC_Z_ZPAGEALLOCATOR_HPP

--- a/src/hotspot/share/gc/z/zPageCache.cpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zPageCache.cpp	Mon Oct 28 11:27:27 2019 +0100
@@ -240,3 +240,26 @@
   flush_list(cl, &_medium, to);
   flush_per_numa_lists(cl, &_small, to);
 }
+
+void ZPageCache::pages_do(ZPageClosure* cl) const {
+  // Small
+  ZPerNUMAConstIterator<ZList<ZPage> > iter_numa(&_small);
+  for (const ZList<ZPage>* list; iter_numa.next(&list);) {
+    ZListIterator<ZPage> iter_small(list);
+    for (ZPage* page; iter_small.next(&page);) {
+      cl->do_page(page);
+    }
+  }
+
+  // Medium
+  ZListIterator<ZPage> iter_medium(&_medium);
+  for (ZPage* page; iter_medium.next(&page);) {
+    cl->do_page(page);
+  }
+
+  // Large
+  ZListIterator<ZPage> iter_large(&_large);
+  for (ZPage* page; iter_large.next(&page);) {
+    cl->do_page(page);
+  }
+}

--- a/src/hotspot/share/gc/z/zPageCache.hpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zPageCache.hpp	Mon Oct 28 11:27:27 2019 +0100
@@ -71,7 +71,7 @@
 
   void flush(ZPageCacheFlushClosure* cl, ZList<ZPage>* to);
 
-  template <typename Closure> void pages_do(Closure* cl) const;
+  void pages_do(ZPageClosure* cl) const;
 };
 
 #endif // SHARE_GC_Z_ZPAGECACHE_HPP

--- a/src/hotspot/share/gc/z/zPageCache.inline.hpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zPageCache.inline.hpp	Mon Oct 28 11:27:27 2019 +0100
@@ -32,28 +32,4 @@
   return _available;
 }
 
-template <typename Closure>
-inline void ZPageCache::pages_do(Closure* cl) const {
-  // Small
-  ZPerNUMAConstIterator<ZList<ZPage> > iter_numa(&_small);
-  for (const ZList<ZPage>* list; iter_numa.next(&list);) {
-    ZListIterator<ZPage> iter_small(list);
-    for (ZPage* page; iter_small.next(&page);) {
-      cl->do_page(page);
-    }
-  }
-
-  // Medium
-  ZListIterator<ZPage> iter_medium(&_medium);
-  for (ZPage* page; iter_medium.next(&page);) {
-    cl->do_page(page);
-  }
-
-  // Large
-  ZListIterator<ZPage> iter_large(&_large);
-  for (ZPage* page; iter_large.next(&page);) {
-    cl->do_page(page);
-  }
-}
-
 #endif // SHARE_GC_Z_ZPAGECACHE_INLINE_HPP

--- a/src/hotspot/share/gc/z/zVerify.cpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zVerify.cpp	Mon Oct 28 11:27:27 2019 +0100
@@ -26,6 +26,7 @@
 #include "gc/z/zAddress.hpp"
 #include "gc/z/zHeap.inline.hpp"
 #include "gc/z/zOop.hpp"
+#include "gc/z/zPageAllocator.hpp"
 #include "gc/z/zResurrection.hpp"
 #include "gc/z/zRootsIterator.hpp"
 #include "gc/z/zStat.hpp"
@@ -170,3 +171,38 @@
   ZStatTimerDisable disable;
   roots_and_objects(true /* verify_weaks */);
 }
+
+template <bool Map>
+class ZPageDebugMapOrUnmapClosure : public ZPageClosure {
+private:
+  const ZPageAllocator* const _allocator;
+
+public:
+  ZPageDebugMapOrUnmapClosure(const ZPageAllocator* allocator) :
+      _allocator(allocator) {}
+
+  void do_page(const ZPage* page) {
+    if (Map) {
+      _allocator->debug_map_page(page);
+    } else {
+      _allocator->debug_unmap_page(page);
+    }
+  }
+};
+
+ZVerifyViewsFlip::ZVerifyViewsFlip(const ZPageAllocator* allocator) :
+    _allocator(allocator) {
+  if (ZVerifyViews) {
+    // Unmap all pages
+    ZPageDebugMapOrUnmapClosure<false /* Map */> cl(_allocator);
+    ZHeap::heap()->pages_do(&cl);
+  }
+}
+
+ZVerifyViewsFlip::~ZVerifyViewsFlip() {
+  if (ZVerifyViews) {
+    // Map all pages
+    ZPageDebugMapOrUnmapClosure<true /* Map */> cl(_allocator);
+    ZHeap::heap()->pages_do(&cl);
+  }
+}

--- a/src/hotspot/share/gc/z/zVerify.hpp	Mon Oct 28 11:26:53 2019 +0100
+++ b/src/hotspot/share/gc/z/zVerify.hpp	Mon Oct 28 11:27:27 2019 +0100
@@ -26,6 +26,8 @@
 
 #include "memory/allocation.hpp"
 
+class ZPageAllocator;
+
 class ZVerify : public AllStatic {
 private:
   template <typename RootsIterator> static void roots();
@@ -45,4 +47,13 @@
   static void after_weak_processing();
 };
 
+class ZVerifyViewsFlip {
+private:
+  const ZPageAllocator* const _allocator;
+
+public:
+  ZVerifyViewsFlip(const ZPageAllocator* allocator);
+  ~ZVerifyViewsFlip();
+};
+
 #endif // SHARE_GC_Z_ZVERIFY_HPP