8370325: G1: Disallow GC for TLAB allocation

Reviewed-by: iwalulya, ayang

Author: Thomas Schatzl

src/hotspot/share/gc/g1/g1CollectedHeap.cpp

@@ -403,21 +403,25 @@ HeapWord* G1CollectedHeap::allocate_new_tlab(size_t min_size,
   assert_heap_not_locked_and_not_at_safepoint();
   assert(!is_humongous(requested_size), "we do not allow humongous TLABs");
 
-  return attempt_allocation(min_size, requested_size, actual_size);
+  // Do not allow a GC because we are allocating a new TLAB to avoid an issue
+  // with UseGCOverheadLimit: although this GC would return null if the overhead
+  // limit would be exceeded, but it would likely free at least some space.
+  // So the subsequent outside-TLAB allocation could be successful anyway and
+  // the indication that the overhead limit had been exceeded swallowed.
+  return attempt_allocation(min_size, requested_size, actual_size, false /* allow_gc */);
 }
 
-HeapWord*
-G1CollectedHeap::mem_allocate(size_t word_size) {
+HeapWord* G1CollectedHeap::mem_allocate(size_t word_size) {
   assert_heap_not_locked_and_not_at_safepoint();
 
   if (is_humongous(word_size)) {
     return attempt_allocation_humongous(word_size);
   }
   size_t dummy = 0;
-  return attempt_allocation(word_size, word_size, &dummy);
+  return attempt_allocation(word_size, word_size, &dummy, true /* allow_gc */);
 }
 
-HeapWord* G1CollectedHeap::attempt_allocation_slow(uint node_index, size_t word_size) {
+HeapWord* G1CollectedHeap::attempt_allocation_slow(uint node_index, size_t word_size, bool allow_gc) {
   ResourceMark rm; // For retrieving the thread names in log messages.
 
   // Make sure you read the note in attempt_allocation_humongous().
@@ -444,6 +448,8 @@ HeapWord* G1CollectedHeap::attempt_allocation_slow(uint node_index, size_t word_
       result = _allocator->attempt_allocation_locked(node_index, word_size);
       if (result != nullptr) {
         return result;
+      } else if (!allow_gc) {
+        return nullptr;
       }
 
       // Read the GC count while still holding the Heap_lock.
@@ -612,7 +618,8 @@ void G1CollectedHeap::dealloc_archive_regions(MemRegion range) {
 
 inline HeapWord* G1CollectedHeap::attempt_allocation(size_t min_word_size,
                                                      size_t desired_word_size,
-                                                     size_t* actual_word_size) {
+                                                     size_t* actual_word_size,
+                                                     bool allow_gc) {
   assert_heap_not_locked_and_not_at_safepoint();
   assert(!is_humongous(desired_word_size), "attempt_allocation() should not "
          "be called for humongous allocation requests");
@@ -624,7 +631,7 @@ inline HeapWord* G1CollectedHeap::attempt_allocation(size_t min_word_size,
 
   if (result == nullptr) {
     *actual_word_size = desired_word_size;
-    result = attempt_allocation_slow(node_index, desired_word_size);
+    result = attempt_allocation_slow(node_index, desired_word_size, allow_gc);
   }
 
   assert_heap_not_locked();

src/hotspot/share/gc/g1/g1CollectedHeap.hpp

@@ -439,18 +439,14 @@ class G1CollectedHeap : public CollectedHeap {
   //
   // * If either call cannot satisfy the allocation request using the
   //   current allocating region, they will try to get a new one. If
-  //   this fails, they will attempt to do an evacuation pause and
-  //   retry the allocation.
-  //
-  // * If all allocation attempts fail, even after trying to schedule
-  //   an evacuation pause, allocate_new_tlab() will return null,
-  //   whereas mem_allocate() will attempt a heap expansion and/or
-  //   schedule a Full GC.
+  //   this fails, (only) mem_allocate() will attempt to do an evacuation
+  //   pause and retry the allocation. Allocate_new_tlab() will return null,
+  //   deferring to the following mem_allocate().
   //
   // * We do not allow humongous-sized TLABs. So, allocate_new_tlab
   //   should never be called with word_size being humongous. All
   //   humongous allocation requests should go to mem_allocate() which
-  //   will satisfy them with a special path.
+  //   will satisfy them in a special path.
 
   HeapWord* allocate_new_tlab(size_t min_size,
                               size_t requested_size,
@@ -463,12 +459,13 @@ class G1CollectedHeap : public CollectedHeap {
   // should only be used for non-humongous allocations.
   inline HeapWord* attempt_allocation(size_t min_word_size,
                                       size_t desired_word_size,
-                                      size_t* actual_word_size);
-
+                                      size_t* actual_word_size,
+                                      bool allow_gc);
   // Second-level mutator allocation attempt: take the Heap_lock and
   // retry the allocation attempt, potentially scheduling a GC
-  // pause. This should only be used for non-humongous allocations.
-  HeapWord* attempt_allocation_slow(uint node_index, size_t word_size);
+  // pause if allow_gc is set. This should only be used for non-humongous
+  // allocations.
+  HeapWord* attempt_allocation_slow(uint node_index, size_t word_size, bool allow_gc);
 
   // Takes the Heap_lock and attempts a humongous allocation. It can
   // potentially schedule a GC pause.