# HG changeset patch
# User sjohanss
# Date 1420642649 -3600
#      Wed Jan 07 15:57:29 2015 +0100
# Node ID 0bfabe254b3990b971043f780701699914c8b3dc
# Parent  8c911031c3e725c92d88a13390625835a180d24e
8062063: Usage of UseHugeTLBFS, UseLargePagesInMetaspace and huge SurvivorAlignmentInBytes cause crashes in CMBitMapClosure::do_bit
Summary: Making sure committed memory is cleared when re-committed, even if using large pages.
Reviewed-by:

diff --git a/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.cpp b/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.cpp
--- a/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.cpp
+++ b/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.cpp
@@ -43,9 +43,11 @@
 # include "os_bsd.inline.hpp"
 #endif
 #include "utilities/bitMap.inline.hpp"
+#include "utilities/copy.hpp"
 
 G1PageBasedVirtualSpace::G1PageBasedVirtualSpace() : _low_boundary(NULL),
-  _high_boundary(NULL), _committed(), _page_size(0), _special(false), _executable(false) {
+  _high_boundary(NULL), _committed(), _page_size(0), _special(false),
+  _needs_clear_on_commit(), _executable(false) {
 }
 
 bool G1PageBasedVirtualSpace::initialize_with_granularity(ReservedSpace rs, size_t page_size) {
@@ -66,6 +68,9 @@
   assert(_committed.size() == 0, "virtual space initialized more than once");
   uintx size_in_bits = rs.size() / page_size;
   _committed.resize(size_in_bits, /* in_resource_area */ false);
+  if (_special) {
+    _needs_clear_on_commit.resize(size_in_bits, /* in_resource_area */ false);
+  }
 
   return true;
 }
@@ -84,6 +89,7 @@
   _executable             = false;
   _page_size              = 0;
   _committed.resize(0, false);
+  _needs_clear_on_commit.resize(0, false);
 }
 
 size_t G1PageBasedVirtualSpace::committed_size() const {
@@ -124,7 +130,17 @@
   // We need to make sure to commit all pages covered by the given area.
   guarantee(is_area_uncommitted(start, size_in_pages), "Specified area is not uncommitted");
 
-  if (!_special) {
+  if (_special) {
+    // When the memory is _special it is not really uncommitted. _needs_clear_on_commit
+    // is used to communicate that the memory needs to be cleared because it is seen by
+    // others as uncommitted.
+    for (uintptr_t page_index = start; page_index < start + size_in_pages; page_index++) {
+      if (_needs_clear_on_commit.at(page_index)) {
+        Copy::zero_to_bytes((HeapWord*)page_start(page_index), _page_size);
+        _needs_clear_on_commit.clear_bit(page_index);
+      }
+    }
+  } else {
     os::commit_memory_or_exit(page_start(start), byte_size_for_pages(size_in_pages), _executable,
                               err_msg("Failed to commit pages from "SIZE_FORMAT" of length "SIZE_FORMAT, start, size_in_pages));
   }
@@ -140,7 +156,10 @@
 MemRegion G1PageBasedVirtualSpace::uncommit(uintptr_t start, size_t size_in_pages) {
   guarantee(is_area_committed(start, size_in_pages), "checking");
 
-  if (!_special) {
+  if (_special) {
+    // Mark that memory needs to be cleared if committed again.
+    _needs_clear_on_commit.set_range(start, start + size_in_pages);
+  } else {
     os::uncommit_memory(page_start(start), byte_size_for_pages(size_in_pages));
   }
 
diff --git a/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.hpp b/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.hpp
--- a/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.hpp
+++ b/src/share/vm/gc_implementation/g1/g1PageBasedVirtualSpace.hpp
@@ -49,6 +49,10 @@
   // Bitmap used for verification of commit/uncommit operations.
   BitMap _committed;
 
+  // For _special spaces we need to keep track if the memory needs to be cleared
+  // on commit or not.
+  BitMap _needs_clear_on_commit;
+
   // Indicates that the entire space has been committed and pinned in memory,
   // os::commit_memory() or os::uncommit_memory() have no function.
   bool _special;