7023069: G1: Introduce symmetric locking in the slow allocation path

7023151: G1: refactor the code that operates on _cur_alloc_region to be re-used for allocs by the GC threads
7018286: G1: humongous allocation attempts should take the GC locker into account

First, this change replaces the asymmetric locking scheme in the G1 slow alloc path by a summetric one. Second, it factors out the code that operates on _cur_alloc_region so that it can be re-used for allocations by the GC threads in the future.

Reviewed-by: stefank, brutisso, johnc

hotspot/src/share/vm/gc_implementation/g1/g1AllocRegion.cpp

@@ -0,0 +1,208 @@
+/*
+ * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "gc_implementation/g1/g1AllocRegion.inline.hpp"
+#include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
+
+G1CollectedHeap* G1AllocRegion::_g1h = NULL;
+HeapRegion* G1AllocRegion::_dummy_region = NULL;
+
+void G1AllocRegion::setup(G1CollectedHeap* g1h, HeapRegion* dummy_region) {
+  assert(_dummy_region == NULL, "should be set once");
+  assert(dummy_region != NULL, "pre-condition");
+  assert(dummy_region->free() == 0, "pre-condition");
+
+  // Make sure that any allocation attempt on this region will fail
+  // and will not trigger any asserts.
+  assert(allocate(dummy_region, 1, false) == NULL, "should fail");
+  assert(par_allocate(dummy_region, 1, false) == NULL, "should fail");
+  assert(allocate(dummy_region, 1, true) == NULL, "should fail");
+  assert(par_allocate(dummy_region, 1, true) == NULL, "should fail");
+
+  _g1h = g1h;
+  _dummy_region = dummy_region;
+}
+
+void G1AllocRegion::fill_up_remaining_space(HeapRegion* alloc_region,
+                                            bool bot_updates) {
+  assert(alloc_region != NULL && alloc_region != _dummy_region,
+         "pre-condition");
+
+  // Other threads might still be trying to allocate using a CAS out
+  // of the region we are trying to retire, as they can do so without
+  // holding the lock. So, we first have to make sure that noone else
+  // can allocate out of it by doing a maximal allocation. Even if our
+  // CAS attempt fails a few times, we'll succeed sooner or later
+  // given that failed CAS attempts mean that the region is getting
+  // closed to being full.
+  size_t free_word_size = alloc_region->free() / HeapWordSize;
+
+  // This is the minimum free chunk we can turn into a dummy
+  // object. If the free space falls below this, then noone can
+  // allocate in this region anyway (all allocation requests will be
+  // of a size larger than this) so we won't have to perform the dummy
+  // allocation.
+  size_t min_word_size_to_fill = CollectedHeap::min_fill_size();
+
+  while (free_word_size >= min_word_size_to_fill) {
+    HeapWord* dummy = par_allocate(alloc_region, free_word_size, bot_updates);
+    if (dummy != NULL) {
+      // If the allocation was successful we should fill in the space.
+      CollectedHeap::fill_with_object(dummy, free_word_size);
+      alloc_region->set_pre_dummy_top(dummy);
+      break;
+    }
+
+    free_word_size = alloc_region->free() / HeapWordSize;
+    // It's also possible that someone else beats us to the
+    // allocation and they fill up the region. In that case, we can
+    // just get out of the loop.
+  }
+  assert(alloc_region->free() / HeapWordSize < min_word_size_to_fill,
+         "post-condition");
+}
+
+void G1AllocRegion::retire(bool fill_up) {
+  assert(_alloc_region != NULL, ar_ext_msg(this, "not initialized properly"));
+
+  trace("retiring");
+  HeapRegion* alloc_region = _alloc_region;
+  if (alloc_region != _dummy_region) {
+    // We never have to check whether the active region is empty or not,
+    // and potentially free it if it is, given that it's guaranteed that
+    // it will never be empty.
+    assert(!alloc_region->is_empty(),
+           ar_ext_msg(this, "the alloc region should never be empty"));
+
+    if (fill_up) {
+      fill_up_remaining_space(alloc_region, _bot_updates);
+    }
+
+    assert(alloc_region->used() >= _used_bytes_before,
+           ar_ext_msg(this, "invariant"));
+    size_t allocated_bytes = alloc_region->used() - _used_bytes_before;
+    retire_region(alloc_region, allocated_bytes);
+    _used_bytes_before = 0;
+    _alloc_region = _dummy_region;
+  }
+  trace("retired");
+}
+
+HeapWord* G1AllocRegion::new_alloc_region_and_allocate(size_t word_size,
+                                                       bool force) {
+  assert(_alloc_region == _dummy_region, ar_ext_msg(this, "pre-condition"));
+  assert(_used_bytes_before == 0, ar_ext_msg(this, "pre-condition"));
+
+  trace("attempting region allocation");
+  HeapRegion* new_alloc_region = allocate_new_region(word_size, force);
+  if (new_alloc_region != NULL) {
+    new_alloc_region->reset_pre_dummy_top();
+    // Need to do this before the allocation
+    _used_bytes_before = new_alloc_region->used();
+    HeapWord* result = allocate(new_alloc_region, word_size, _bot_updates);
+    assert(result != NULL, ar_ext_msg(this, "the allocation should succeeded"));
+
+    OrderAccess::storestore();
+    // Note that we first perform the allocation and then we store the
+    // region in _alloc_region. This is the reason why an active region
+    // can never be empty.
+    _alloc_region = new_alloc_region;
+    trace("region allocation successful");
+    return result;
+  } else {
+    trace("region allocation failed");
+    return NULL;
+  }
+  ShouldNotReachHere();
+}
+
+void G1AllocRegion::fill_in_ext_msg(ar_ext_msg* msg, const char* message) {
+  msg->append("[%s] %s b: %s r: "PTR_FORMAT" u: "SIZE_FORMAT,
+              _name, message, BOOL_TO_STR(_bot_updates),
+              _alloc_region, _used_bytes_before);
+}
+
+void G1AllocRegion::init() {
+  trace("initializing");
+  assert(_alloc_region == NULL && _used_bytes_before == 0,
+         ar_ext_msg(this, "pre-condition"));
+  assert(_dummy_region != NULL, "should have been set");
+  _alloc_region = _dummy_region;
+  trace("initialized");
+}
+
+HeapRegion* G1AllocRegion::release() {
+  trace("releasing");
+  HeapRegion* alloc_region = _alloc_region;
+  retire(false /* fill_up */);
+  assert(_alloc_region == _dummy_region, "post-condition of retire()");
+  _alloc_region = NULL;
+  trace("released");
+  return (alloc_region == _dummy_region) ? NULL : alloc_region;
+}
+
+#if G1_ALLOC_REGION_TRACING
+void G1AllocRegion::trace(const char* str, size_t word_size, HeapWord* result) {
+  // All the calls to trace that set either just the size or the size
+  // and the result are considered part of level 2 tracing and are
+  // skipped during level 1 tracing.
+  if ((word_size == 0 && result == NULL) || (G1_ALLOC_REGION_TRACING > 1)) {
+    const size_t buffer_length = 128;
+    char hr_buffer[buffer_length];
+    char rest_buffer[buffer_length];
+
+    HeapRegion* alloc_region = _alloc_region;
+    if (alloc_region == NULL) {
+      jio_snprintf(hr_buffer, buffer_length, "NULL");
+    } else if (alloc_region == _dummy_region) {
+      jio_snprintf(hr_buffer, buffer_length, "DUMMY");
+    } else {
+      jio_snprintf(hr_buffer, buffer_length,
+                   HR_FORMAT, HR_FORMAT_PARAMS(alloc_region));
+    }
+
+    if (G1_ALLOC_REGION_TRACING > 1) {
+      if (result != NULL) {
+        jio_snprintf(rest_buffer, buffer_length, SIZE_FORMAT" "PTR_FORMAT,
+                     word_size, result);
+      } else if (word_size != 0) {
+        jio_snprintf(rest_buffer, buffer_length, SIZE_FORMAT, word_size);
+      } else {
+        jio_snprintf(rest_buffer, buffer_length, "");
+      }
+    } else {
+      jio_snprintf(rest_buffer, buffer_length, "");
+    }
+
+    tty->print_cr("[%s] %s : %s %s", _name, hr_buffer, str, rest_buffer);
+  }
+}
+#endif // G1_ALLOC_REGION_TRACING
+
+G1AllocRegion::G1AllocRegion(const char* name,
+                             bool bot_updates)
+  : _name(name), _bot_updates(bot_updates),
+    _alloc_region(NULL), _used_bytes_before(0) { }
+