Author: [email protected]
Date: Thu May 7 05:36:18 2009
New Revision: 1900
Modified:
branches/bleeding_edge/src/heap.cc
branches/bleeding_edge/src/spaces.h
Log:
Change the structure of the scavenge collector's loop. Move
scavenging of objects pointed to by weak handles earlier. Rename
"mark" => "front" and "top" => "rear" to make it clearer which end is
which.
Review URL: http://codereview.chromium.org/113097
Modified: branches/bleeding_edge/src/heap.cc
==============================================================================
--- branches/bleeding_edge/src/heap.cc (original)
+++ branches/bleeding_edge/src/heap.cc Thu May 7 05:36:18 2009
@@ -538,7 +538,7 @@
// Shared state read by the scavenge collector and set by ScavengeObject.
-static Address promoted_top = NULL;
+static Address promoted_rear = NULL;
#ifdef DEBUG
@@ -606,72 +606,70 @@
new_space_.Flip();
new_space_.ResetAllocationInfo();
- // We need to sweep newly copied objects which can be in either the to
space
- // or the old space. For to space objects, we use a mark. Newly copied
- // objects lie between the mark and the allocation top. For objects
- // promoted to old space, we write their addresses downward from the top
of
- // the new space. Sweeping newly promoted objects requires an allocation
- // pointer and a mark. Note that the allocation pointer 'top' actually
- // moves downward from the high address in the to space.
+ // We need to sweep newly copied objects which can be either in the
+ // to space or promoted to the old generation. For to-space
+ // objects, we treat the bottom of the to space as a queue. Newly
+ // copied and unswept objects lie between a 'front' mark and the
+ // allocation pointer.
//
- // There is guaranteed to be enough room at the top of the to space for
the
- // addresses of promoted objects: every object promoted frees up its
size in
- // bytes from the top of the new space, and objects are at least one
pointer
- // in size. Using the new space to record promoted addresses makes the
- // scavenge collector agnostic to the allocation strategy (eg, linear or
- // free-list) used in old space.
- Address new_mark = new_space_.ToSpaceLow();
- Address promoted_mark = new_space_.ToSpaceHigh();
- promoted_top = new_space_.ToSpaceHigh();
+ // Promoted objects can go into various old-generation spaces, and
+ // can be allocated internally in the spaces (from the free list).
+ // We treat the top of the to space as a queue of addresses of
+ // promoted objects. The addresses of newly promoted and unswept
+ // objects lie between a 'front' mark and a 'rear' mark that is
+ // updated as a side effect of promoting an object.
+ //
+ // There is guaranteed to be enough room at the top of the to space
+ // for the addresses of promoted objects: every object promoted
+ // frees up its size in bytes from the top of the new space, and
+ // objects are at least one pointer in size.
+ Address new_space_front = new_space_.ToSpaceLow();
+ Address promoted_front = new_space_.ToSpaceHigh();
+ promoted_rear = new_space_.ToSpaceHigh();
ScavengeVisitor scavenge_visitor;
// Copy roots.
IterateRoots(&scavenge_visitor);
- // Copy objects reachable from the old generation. By definition, there
- // are no intergenerational pointers in code or data spaces.
+ // Copy objects reachable from weak pointers.
+ GlobalHandles::IterateWeakRoots(&scavenge_visitor);
+
+ // Copy objects reachable from the old generation. By definition,
+ // there are no intergenerational pointers in code or data spaces.
IterateRSet(old_pointer_space_, &ScavengePointer);
IterateRSet(map_space_, &ScavengePointer);
lo_space_->IterateRSet(&ScavengePointer);
- bool has_processed_weak_pointers = false;
-
- while (true) {
- ASSERT(new_mark <= new_space_.top());
- ASSERT(promoted_mark >= promoted_top);
-
- // Copy objects reachable from newly copied objects.
- while (new_mark < new_space_.top() || promoted_mark > promoted_top) {
- // Sweep newly copied objects in the to space. The allocation
pointer
- // can change during sweeping.
- Address previous_top = new_space_.top();
- SemiSpaceIterator new_it(new_space(), new_mark);
- while (new_it.has_next()) {
- new_it.next()->Iterate(&scavenge_visitor);
- }
- new_mark = previous_top;
+ do {
+ ASSERT(new_space_front <= new_space_.top());
+ ASSERT(promoted_front >= promoted_rear);
+
+ // The addresses new_space_front and new_space_.top() define a
+ // queue of unprocessed copied objects. Process them until the
+ // queue is empty.
+ while (new_space_front < new_space_.top()) {
+ HeapObject* object = HeapObject::FromAddress(new_space_front);
+ object->Iterate(&scavenge_visitor);
+ new_space_front += object->Size();
+ }
- // Sweep newly copied objects in the old space. The promotion 'top'
- // pointer could change during sweeping.
- previous_top = promoted_top;
- for (Address current = promoted_mark - kPointerSize;
- current >= previous_top;
- current -= kPointerSize) {
- HeapObject* object = HeapObject::cast(Memory::Object_at(current));
- object->Iterate(&scavenge_visitor);
- UpdateRSet(object);
- }
- promoted_mark = previous_top;
+ // The addresses promoted_front and promoted_rear define a queue
+ // of unprocessed addresses of promoted objects. Process them
+ // until the queue is empty.
+ while (promoted_front > promoted_rear) {
+ promoted_front -= kPointerSize;
+ HeapObject* object =
+ HeapObject::cast(Memory::Object_at(promoted_front));
+ object->Iterate(&scavenge_visitor);
+ UpdateRSet(object);
}
- if (has_processed_weak_pointers) break; // We are done.
- // Copy objects reachable from weak pointers.
- GlobalHandles::IterateWeakRoots(&scavenge_visitor);
- has_processed_weak_pointers = true;
- }
+ // Take another spin if there are now unswept objects in new space
+ // (there are currently no more unswept promoted objects).
+ } while (new_space_front < new_space_.top());
// Set age mark.
- new_space_.set_age_mark(new_mark);
+ new_space_.set_age_mark(new_space_.top());
LOG(ResourceEvent("scavenge", "end"));
@@ -892,8 +890,8 @@
if (target_space == Heap::old_pointer_space_) {
// Record the object's address at the top of the to space, to allow
// it to be swept by the scavenger.
- promoted_top -= kPointerSize;
- Memory::Object_at(promoted_top) = *p;
+ promoted_rear -= kPointerSize;
+ Memory::Object_at(promoted_rear) = *p;
} else {
#ifdef DEBUG
// Objects promoted to the data space should not have pointers to
Modified: branches/bleeding_edge/src/spaces.h
==============================================================================
--- branches/bleeding_edge/src/spaces.h (original)
+++ branches/bleeding_edge/src/spaces.h Thu May 7 05:36:18 2009
@@ -517,7 +517,7 @@
// allocating new objects), the iterator does not iterate objects
// above the original space top. The caller must create a new
// iterator starting from the old top in order to visit these new
-// objects. Heap::Scavenge() is such an example.
+// objects.
//
// (2) If new objects are allocated below the original allocation top
// (e.g., free-list allocation in paged spaces), the new objects
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