commit 6e6078ab06e16bb4032b363316360f3b76685e30
author Mathieu Chartier <mathieuc@google.com> Mon Oct 24 15:45:41 2016 -0700
committer Mathieu Chartier <mathieuc@google.com> Mon Oct 24 19:23:06 2016 -0700
tree 539b5b28159f2b8e6a3893b03915c65c91474761
parent 3209925b7c0e173741885e63f747af16dac78469

Clear (madvise) card table for CC

Since the cards are not really used, we can madvise them to reduce
RAM. Image and zygote cards are cleared in pause to prevent races
between with mutators.

Pause time goes up by only 1.5us on N6P maps:
(Paused)ClearCards: Sum: 755us 99% C.I. 0.250us-28us Avg: 1.540us Max: 28us

AOSP N6P before (60s after boot system wide CC):
4,194K: .GC
4,172K: .GC
4,110K: .GC

After:
3,253K: .GC
3,205K: .GC
3,245K: .GC

Bug: 12687968

Test: test-art-host

Change-Id: I3194b5b8044c2dca427302c32d9974920fecb289

runtime/gc/accounting/mod_union_table.h

diff --git a/runtime/gc/accounting/mod_union_table.h b/runtime/gc/accounting/mod_union_table.h
index b6792c4..591365f 100644
--- a/runtime/gc/accounting/mod_union_table.h
+++ b/runtime/gc/accounting/mod_union_table.h
@@ -55,10 +55,10 @@
 
   virtual ~ModUnionTable() {}
 
-  // Clear cards which map to a memory range of a space. This doesn't immediately update the
-  // mod-union table, as updating the mod-union table may have an associated cost, such as
-  // determining references to track.
-  virtual void ClearCards() = 0;
+  // Process cards for a memory range of a space. This doesn't immediately update the mod-union
+  // table, as updating the mod-union table may have an associated cost, such as determining
+  // references to track.
+  virtual void ProcessCards() = 0;
 
   // Set all the cards.
   virtual void SetCards() = 0;
@@ -66,9 +66,9 @@
   // Clear all of the table.
   virtual void ClearTable() = 0;
 
-  // Update the mod-union table using data stored by ClearCards. There may be multiple ClearCards
-  // before a call to update, for example, back-to-back sticky GCs. Also mark references to other
-  // spaces which are stored in the mod-union table.
+  // Update the mod-union table using data stored by ProcessCards. There may be multiple
+  // ProcessCards before a call to update, for example, back-to-back sticky GCs. Also mark
+  // references to other spaces which are stored in the mod-union table.
   virtual void UpdateAndMarkReferences(MarkObjectVisitor* visitor) = 0;
 
   // Visit all of the objects that may contain references to other spaces.
@@ -117,7 +117,7 @@
   virtual ~ModUnionTableReferenceCache() {}
 
   // Clear and store cards for a space.
-  void ClearCards() OVERRIDE;
+  void ProcessCards() OVERRIDE;
 
   // Update table based on cleared cards and mark all references to the other spaces.
   void UpdateAndMarkReferences(MarkObjectVisitor* visitor) OVERRIDE
@@ -164,7 +164,7 @@
   virtual ~ModUnionTableCardCache() {}
 
   // Clear and store cards for a space.
-  virtual void ClearCards() OVERRIDE;
+  virtual void ProcessCards() OVERRIDE;
 
   // Mark all references to the alloc space(s).
   virtual void UpdateAndMarkReferences(MarkObjectVisitor* visitor) OVERRIDE