8315219: G1: Improve allocator pathological case where it keeps doing…

… direct allocations instead of retiring a PLAB

Reviewed-by: tschatzl, ayang, mli

src/hotspot/share/gc/g1/g1Allocator.cpp

@@ -358,14 +358,18 @@ G1PLABAllocator::G1PLABAllocator(G1Allocator* allocator) :
   }
 }
 
-bool G1PLABAllocator::may_throw_away_buffer(size_t const allocation_word_sz, size_t const buffer_size) const {
-  return (allocation_word_sz * 100 < buffer_size * ParallelGCBufferWastePct);
+bool G1PLABAllocator::may_throw_away_buffer(size_t const words_remaining, size_t const buffer_size) const {
+  return (words_remaining * 100 < buffer_size * ParallelGCBufferWastePct);
 }
 
 HeapWord* G1PLABAllocator::allocate_direct_or_new_plab(G1HeapRegionAttr dest,
                                                        size_t word_sz,
                                                        bool* plab_refill_failed,
                                                        uint node_index) {
+  PLAB* alloc_buf = alloc_buffer(dest, node_index);
+  size_t words_remaining = alloc_buf->words_remaining();
+  assert(words_remaining < word_sz, "precondition");
+
   size_t plab_word_size = plab_size(dest.type());
   size_t next_plab_word_size = plab_word_size;
 
@@ -378,13 +382,10 @@ HeapWord* G1PLABAllocator::allocate_direct_or_new_plab(G1HeapRegionAttr dest,
   size_t required_in_plab = PLAB::size_required_for_allocation(word_sz);
 
   // Only get a new PLAB if the allocation fits into the to-be-allocated PLAB and
-  // it would not waste more than ParallelGCBufferWastePct in the current PLAB.
-  // Boosting the PLAB also increasingly allows more waste to occur.
+  // retiring the current PLAB would not waste more than ParallelGCBufferWastePct
+  // in the current PLAB. Boosting the PLAB also increasingly allows more waste to occur.
   if ((required_in_plab <= next_plab_word_size) &&
-    may_throw_away_buffer(required_in_plab, plab_word_size)) {
-
-    PLAB* alloc_buf = alloc_buffer(dest, node_index);
-    guarantee(alloc_buf->words_remaining() <= required_in_plab, "must be");
+    may_throw_away_buffer(words_remaining, plab_word_size)) {
 
     alloc_buf->retire();
 

test/hotspot/jtreg/gc/g1/plab/TestPLABPromotion.java

@@ -45,6 +45,7 @@
 import gc.g1.plab.lib.PLABUtils;
 import gc.g1.plab.lib.PlabInfo;
 
+import jdk.test.lib.Platform;
 import jdk.test.lib.process.OutputAnalyzer;
 import jdk.test.lib.process.ProcessTools;
 
@@ -62,17 +63,18 @@ public class TestPLABPromotion {
     private final static String PLAB_DIRECT_ALLOCATED_FIELD_NAME = "direct allocated";
     private final static List<String> FIELDS_TO_EXTRACT = Arrays.asList(PLAB_USED_FIELD_NAME, PLAB_DIRECT_ALLOCATED_FIELD_NAME);
 
+    private static final int HEAP_WORD_SIZE = Platform.is32bit() ? 4 : 8;
+
     private static String output;
 
     // Allowable difference for memory consumption (percentage)
     private final static long MEM_DIFFERENCE_PCT = 5;
-
     private static final int PLAB_SIZE_SMALL = 1024;
     private static final int PLAB_SIZE_MEDIUM = 4096;
     private static final int PLAB_SIZE_HIGH = 65536;
-    private static final int OBJECT_SIZE_SMALL = 10;
-    private static final int OBJECT_SIZE_MEDIUM = 100;
-    private static final int OBJECT_SIZE_HIGH = 3250;
+    private static final int OBJECT_SIZE_SMALL  = 10 * HEAP_WORD_SIZE;
+    private static final int OBJECT_SIZE_MEDIUM = 128 * HEAP_WORD_SIZE;
+    private static final int OBJECT_SIZE_HIGH   = 3072 * HEAP_WORD_SIZE;
     private static final int GC_NUM_SMALL = 1;
     private static final int GC_NUM_MEDIUM = 3;
     private static final int GC_NUM_HIGH = 7;
@@ -94,7 +96,8 @@ public class TestPLABPromotion {
         new TestCase(WASTE_PCT_SMALL, PLAB_SIZE_SMALL, OBJECT_SIZE_HIGH, GC_NUM_MEDIUM, YOUNG_SIZE_LOW, PLAB_FIXED, true, false),
         new TestCase(WASTE_PCT_MEDIUM, PLAB_SIZE_HIGH, OBJECT_SIZE_SMALL, GC_NUM_HIGH, YOUNG_SIZE_HIGH, PLAB_FIXED, true, true),
         new TestCase(WASTE_PCT_MEDIUM, PLAB_SIZE_SMALL, OBJECT_SIZE_MEDIUM, GC_NUM_SMALL, YOUNG_SIZE_LOW, PLAB_FIXED, true, true),
-        new TestCase(WASTE_PCT_MEDIUM, PLAB_SIZE_MEDIUM, OBJECT_SIZE_HIGH, GC_NUM_MEDIUM, YOUNG_SIZE_LOW, PLAB_FIXED, true, true),
+        new TestCase(WASTE_PCT_MEDIUM, PLAB_SIZE_MEDIUM, OBJECT_SIZE_HIGH, GC_NUM_MEDIUM, YOUNG_SIZE_LOW, PLAB_FIXED, true, false),
+        new TestCase(WASTE_PCT_HIGH, PLAB_SIZE_MEDIUM, OBJECT_SIZE_HIGH, GC_NUM_MEDIUM, YOUNG_SIZE_LOW, PLAB_FIXED, true, true),
         new TestCase(WASTE_PCT_HIGH, PLAB_SIZE_SMALL, OBJECT_SIZE_SMALL, GC_NUM_HIGH, YOUNG_SIZE_HIGH, PLAB_FIXED, true, true),
         new TestCase(WASTE_PCT_HIGH, PLAB_SIZE_HIGH, OBJECT_SIZE_MEDIUM, GC_NUM_SMALL, YOUNG_SIZE_LOW, PLAB_FIXED, true, true),
         new TestCase(WASTE_PCT_HIGH, PLAB_SIZE_SMALL, OBJECT_SIZE_HIGH, GC_NUM_MEDIUM, YOUNG_SIZE_HIGH, PLAB_FIXED, true, false),
@@ -104,8 +107,6 @@ public class TestPLABPromotion {
         new TestCase(WASTE_PCT_SMALL, PLAB_SIZE_HIGH, OBJECT_SIZE_SMALL, GC_NUM_HIGH, YOUNG_SIZE_HIGH, PLAB_DYNAMIC, true, true),
         new TestCase(WASTE_PCT_MEDIUM, PLAB_SIZE_MEDIUM, OBJECT_SIZE_SMALL, GC_NUM_SMALL, YOUNG_SIZE_LOW, PLAB_DYNAMIC, true, true),
         new TestCase(WASTE_PCT_SMALL, PLAB_SIZE_MEDIUM, OBJECT_SIZE_HIGH, GC_NUM_HIGH, YOUNG_SIZE_HIGH, PLAB_DYNAMIC, true, false),
-        new TestCase(WASTE_PCT_MEDIUM, PLAB_SIZE_SMALL, OBJECT_SIZE_MEDIUM, GC_NUM_MEDIUM, YOUNG_SIZE_LOW, PLAB_DYNAMIC, true, true),
-        new TestCase(WASTE_PCT_HIGH, PLAB_SIZE_HIGH, OBJECT_SIZE_MEDIUM, GC_NUM_SMALL, YOUNG_SIZE_HIGH, PLAB_DYNAMIC, true, true),
         new TestCase(WASTE_PCT_HIGH, PLAB_SIZE_HIGH, OBJECT_SIZE_SMALL, GC_NUM_HIGH, YOUNG_SIZE_LOW, PLAB_DYNAMIC, true, true)
     };