# HG changeset patch
# Parent e8aaebb625973b71c265d758e4964eb8d7a22320
# User tschatzl

diff -r e8aaebb62597 src/share/vm/gc/g1/g1RegionToSpaceMapper.cpp
--- a/src/share/vm/gc/g1/g1RegionToSpaceMapper.cpp	Tue Apr 21 15:35:24 2015 +0200
+++ b/src/share/vm/gc/g1/g1RegionToSpaceMapper.cpp	Tue Apr 21 15:35:48 2015 +0200
@@ -26,6 +26,7 @@
 #include "gc/g1/g1BiasedArray.hpp"
 #include "gc/g1/g1RegionToSpaceMapper.hpp"
 #include "memory/allocation.inline.hpp"
+#include "memory/resourceArea.hpp"
 #include "runtime/virtualspace.hpp"
 #include "services/memTracker.hpp"
 #include "utilities/bitMap.inline.hpp"
@@ -112,17 +113,51 @@
   }
 
   virtual void commit_regions(uint start_idx, size_t num_regions) {
+    // The algorithm to commit tries to merge commits to multiple pages into as
+    // few as possible commit calls to the OS.
+    // For this to work, we make multiple passes over the memory range: first we
+    // record the pages that actually need to be committed (in the want_to_commit
+    // bitmap) from the OS, then walk over this bitmap to commit and determine which
+    // of those were zero-filled, to later determine the correct value of the
+    // zero_filled parameter in the calls to the listener for the particular region.
+
+    ResourceMark rm; // We allocate temporary bitmaps in the resource area.
+
+    BitMap want_to_commit(_refcounts.length());
+    want_to_commit.clear();
+
     for (uint i = start_idx; i < start_idx + num_regions; i++) {
       assert(!_commit_map.at(i), err_msg("Trying to commit storage at region %u that is already committed", i));
       size_t idx = region_idx_to_page_idx(i);
       uint old_refcount = _refcounts.get_by_index(idx);
-      bool zero_filled = false;
       if (old_refcount == 0) {
-        zero_filled = _storage.commit(idx, 1);
+        want_to_commit.set_bit(idx);
       }
       _refcounts.set_by_index(idx, old_refcount + 1);
       _commit_map.set_bit(i);
-      fire_on_commit(i, 1, zero_filled);
+    }
+
+    BitMap just_committed_zero_filled_answer(_refcounts.length());
+    just_committed_zero_filled_answer.clear();
+
+    // Iterate over the want_to_commit page table to do the commit call and gather
+    // whether the committed area is already zero filled.
+    BitMap::idx_t want_commit_start = want_to_commit.get_next_one_offset(0);
+    while (want_commit_start != want_to_commit.size()) {
+      BitMap::idx_t want_commit_end = want_to_commit.get_next_zero_offset(want_commit_start + 1);
+      size_t len_to_commit = want_commit_end - want_commit_start;
+      guarantee(len_to_commit > 0, "must be");
+
+      bool zero_filled = _storage.commit(want_commit_start, len_to_commit);
+      if (zero_filled) {
+        just_committed_zero_filled_answer.set_range(want_commit_start, want_commit_end);
+      }
+      want_commit_start = want_to_commit.get_next_one_offset(want_commit_end);
+    }
+
+    // Call the listeners with the appropriate values.
+    for (uint i = start_idx; i < start_idx + num_regions; i++) {
+      fire_on_commit(i, 1, just_committed_zero_filled_answer.at(region_idx_to_page_idx(i)));
     }
   }