6974966: G1: unnecessary direct-to-old allocations

This change revamps the slow allocation path of G1. Improvements include the following: a) Allocations directly to old regions are now totally banned. G1 now only allows allocations out of young regions (with the only exception being humongous regions). b) The thread that allocates a new region (which is now guaranteed to be young) does not dirty all its cards. Each thread that successfully allocates out of a young region is now responsible for dirtying the cards that corresponding to the "block" that just got allocated. c) allocate_new_tlab() and mem_allocate() are now implemented differently and TLAB allocations are only done by allocate_new_tlab(). d) If a thread schedules an evacuation pause in order to satisfy an allocation request, it will perform the allocation at the end of the safepoint so that the thread that initiated the GC also gets "first pick" of any space made available by the GC. e) If a thread is unable to allocate a humongous object it will schedule an evacuation pause in case it reclaims enough regions so that the humongous allocation can be satisfied aftewards. f) The G1 policy is more careful to set the young list target length to be the survivor number +1. g) Lots of code tidy up, removal, refactoring to make future changes easier.

Reviewed-by: johnc, ysr

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.inline.hpp

@@ -27,6 +27,7 @@
 
 #include "gc_implementation/g1/concurrentMark.hpp"
 #include "gc_implementation/g1/g1CollectedHeap.hpp"
+#include "gc_implementation/g1/g1CollectorPolicy.hpp"
 #include "gc_implementation/g1/heapRegionSeq.hpp"
 #include "utilities/taskqueue.hpp"
 
@@ -58,37 +59,114 @@ inline bool G1CollectedHeap::obj_in_cs(oop obj) {
   return r != NULL && r->in_collection_set();
 }
 
-inline HeapWord* G1CollectedHeap::attempt_allocation(size_t word_size,
-                                              bool permit_collection_pause) {
-  HeapWord* res = NULL;
+// See the comment in the .hpp file about the locking protocol and
+// assumptions of this method (and other related ones).
+inline HeapWord*
+G1CollectedHeap::allocate_from_cur_alloc_region(HeapRegion* cur_alloc_region,
+                                                size_t word_size) {
+  assert_heap_locked_and_not_at_safepoint();
+  assert(cur_alloc_region != NULL, "pre-condition of the method");
+  assert(cur_alloc_region == _cur_alloc_region, "pre-condition of the method");
+  assert(cur_alloc_region->is_young(),
+         "we only support young current alloc regions");
+  assert(!isHumongous(word_size), "allocate_from_cur_alloc_region() "
+         "should not be used for humongous allocations");
+  assert(!cur_alloc_region->isHumongous(), "Catch a regression of this bug.");
 
-  assert( SafepointSynchronize::is_at_safepoint() ||
-          Heap_lock->owned_by_self(), "pre-condition of the call" );
+  assert(!cur_alloc_region->is_empty(),
+         err_msg("region ["PTR_FORMAT","PTR_FORMAT"] should not be empty",
+                 cur_alloc_region->bottom(), cur_alloc_region->end()));
+  // This allocate method does BOT updates and we don't need them in
+  // the young generation. This will be fixed in the near future by
+  // CR 6994297.
+  HeapWord* result = cur_alloc_region->allocate(word_size);
+  if (result != NULL) {
+    assert(is_in(result), "result should be in the heap");
+    Heap_lock->unlock();
 
-  // All humongous allocation requests should go through the slow path in
-  // attempt_allocation_slow().
-  if (!isHumongous(word_size) && _cur_alloc_region != NULL) {
-    // If this allocation causes a region to become non empty,
-    // then we need to update our free_regions count.
-
-    if (_cur_alloc_region->is_empty()) {
-      res = _cur_alloc_region->allocate(word_size);
-      if (res != NULL)
-        _free_regions--;
-    } else {
-      res = _cur_alloc_region->allocate(word_size);
-    }
-
-    if (res != NULL) {
-      if (!SafepointSynchronize::is_at_safepoint()) {
-        assert( Heap_lock->owned_by_self(), "invariant" );
-        Heap_lock->unlock();
-      }
-      return res;
-    }
+    // Do the dirtying after we release the Heap_lock.
+    dirty_young_block(result, word_size);
+    return result;
   }
-  // attempt_allocation_slow will also unlock the heap lock when appropriate.
-  return attempt_allocation_slow(word_size, permit_collection_pause);
+
+  assert_heap_locked();
+  return NULL;
+}
+
+// See the comment in the .hpp file about the locking protocol and
+// assumptions of this method (and other related ones).
+inline HeapWord*
+G1CollectedHeap::attempt_allocation(size_t word_size) {
+  assert_heap_locked_and_not_at_safepoint();
+  assert(!isHumongous(word_size), "attempt_allocation() should not be called "
+         "for humongous allocation requests");
+
+  HeapRegion* cur_alloc_region = _cur_alloc_region;
+  if (cur_alloc_region != NULL) {
+    HeapWord* result = allocate_from_cur_alloc_region(cur_alloc_region,
+                                                      word_size);
+    if (result != NULL) {
+      assert_heap_not_locked();
+      return result;
+    }
+
+    assert_heap_locked();
+
+    // Since we couldn't successfully allocate into it, retire the
+    // current alloc region.
+    retire_cur_alloc_region(cur_alloc_region);
+  }
+
+  // Try to get a new region and allocate out of it
+  HeapWord* result = replace_cur_alloc_region_and_allocate(word_size,
+                                                      false, /* at safepoint */
+                                                      true   /* do_dirtying */);
+  if (result != NULL) {
+    assert_heap_not_locked();
+    return result;
+  }
+
+  assert_heap_locked();
+  return NULL;
+}
+
+inline void
+G1CollectedHeap::retire_cur_alloc_region_common(HeapRegion* cur_alloc_region) {
+  assert_heap_locked_or_at_safepoint();
+  assert(cur_alloc_region != NULL && cur_alloc_region == _cur_alloc_region,
+         "pre-condition of the call");
+  assert(cur_alloc_region->is_young(),
+         "we only support young current alloc regions");
+
+  // The region is guaranteed to be young
+  g1_policy()->add_region_to_incremental_cset_lhs(cur_alloc_region);
+  _summary_bytes_used += cur_alloc_region->used();
+  _cur_alloc_region = NULL;
+}
+
+// It dirties the cards that cover the block so that so that the post
+// write barrier never queues anything when updating objects on this
+// block. It is assumed (and in fact we assert) that the block
+// belongs to a young region.
+inline void
+G1CollectedHeap::dirty_young_block(HeapWord* start, size_t word_size) {
+  assert_heap_not_locked();
+
+  // Assign the containing region to containing_hr so that we don't
+  // have to keep calling heap_region_containing_raw() in the
+  // asserts below.
+  DEBUG_ONLY(HeapRegion* containing_hr = heap_region_containing_raw(start);)
+  assert(containing_hr != NULL && start != NULL && word_size > 0,
+         "pre-condition");
+  assert(containing_hr->is_in(start), "it should contain start");
+  assert(containing_hr->is_young(), "it should be young");
+  assert(!containing_hr->isHumongous(), "it should not be humongous");
+
+  HeapWord* end = start + word_size;
+  assert(containing_hr->is_in(end - 1), "it should also contain end - 1");
+
+  MemRegion mr(start, end);
+  ((CardTableModRefBS*)_g1h->barrier_set())->dirty(mr);
 }
 
 inline RefToScanQueue* G1CollectedHeap::task_queue(int i) const {