src/share/vm/gc_implementation/g1/g1BiasedArray.cpp

Fri, 10 Oct 2014 15:51:58 +0200

author
tschatzl
date
Fri, 10 Oct 2014 15:51:58 +0200
changeset 7257
e7d0505c8a30
parent 6680
78bbf4d43a14
child 6876
710a3c8b516e
child 9327
f96fcd9e1e1b
permissions
-rw-r--r--

8059758: Footprint regressions with JDK-8038423
Summary: Changes in JDK-8038423 always initialize (zero out) virtual memory used for auxiliary data structures. This causes a footprint regression for G1 in startup benchmarks. This is because they do not touch that memory at all, so the operating system does not actually commit these pages. The fix is to, if the initialization value of the data structures matches the default value of just committed memory (=0), do not do anything.
Reviewed-by: jwilhelm, brutisso

     1 /*
     2  * Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.
     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
     4  *
     5  * This code is free software; you can redistribute it and/or modify it
     6  * under the terms of the GNU General Public License version 2 only, as
     7  * published by the Free Software Foundation.
     8  *
     9  * This code is distributed in the hope that it will be useful, but WITHOUT
    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    12  * version 2 for more details (a copy is included in the LICENSE file that
    13  * accompanied this code).
    14  *
    15  * You should have received a copy of the GNU General Public License version
    16  * 2 along with this work; if not, write to the Free Software Foundation,
    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
    18  *
    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
    20  * or visit www.oracle.com if you need additional information or have any
    21  * questions.
    22  *
    23  */
    25 #include "precompiled.hpp"
    26 #include "gc_implementation/g1/g1BiasedArray.hpp"
    27 #include "memory/padded.inline.hpp"
    29 // Allocate a new array, generic version.
    30 address G1BiasedMappedArrayBase::create_new_base_array(size_t length, size_t elem_size) {
    31   assert(length > 0, "just checking");
    32   assert(elem_size > 0, "just checking");
    33   return PaddedPrimitiveArray<u_char, mtGC>::create_unfreeable(length * elem_size);
    34 }
    36 #ifndef PRODUCT
    37 void G1BiasedMappedArrayBase::verify_index(idx_t index) const {
    38   guarantee(_base != NULL, "Array not initialized");
    39   guarantee(index < length(), err_msg("Index out of bounds index: "SIZE_FORMAT" length: "SIZE_FORMAT, index, length()));
    40 }
    42 void G1BiasedMappedArrayBase::verify_biased_index(idx_t biased_index) const {
    43   guarantee(_biased_base != NULL, "Array not initialized");
    44   guarantee(biased_index >= bias() && biased_index < (bias() + length()),
    45     err_msg("Biased index out of bounds, index: "SIZE_FORMAT" bias: "SIZE_FORMAT" length: "SIZE_FORMAT, biased_index, bias(), length()));
    46 }
    48 void G1BiasedMappedArrayBase::verify_biased_index_inclusive_end(idx_t biased_index) const {
    49   guarantee(_biased_base != NULL, "Array not initialized");
    50   guarantee(biased_index >= bias() && biased_index <= (bias() + length()),
    51     err_msg("Biased index out of inclusive bounds, index: "SIZE_FORMAT" bias: "SIZE_FORMAT" length: "SIZE_FORMAT, biased_index, bias(), length()));
    52 }
    54 class TestMappedArray : public G1BiasedMappedArray<int> {
    55 protected:
    56   virtual int default_value() const { return 0xBAADBABE; }
    57 public:
    58   static void test_biasedarray() {
    59     const size_t REGION_SIZE_IN_WORDS = 512;
    60     const size_t NUM_REGIONS = 20;
    61     HeapWord* fake_heap = (HeapWord*)LP64_ONLY(0xBAAA00000) NOT_LP64(0xBA000000); // Any value that is non-zero
    63     TestMappedArray array;
    64     array.initialize(fake_heap, fake_heap + REGION_SIZE_IN_WORDS * NUM_REGIONS,
    65             REGION_SIZE_IN_WORDS * HeapWordSize);
    66     // Check address calculation (bounds)
    67     assert(array.bottom_address_mapped() == fake_heap,
    68       err_msg("bottom mapped address should be " PTR_FORMAT ", but is " PTR_FORMAT, p2i(fake_heap), p2i(array.bottom_address_mapped())));
    69     assert(array.end_address_mapped() == (fake_heap + REGION_SIZE_IN_WORDS * NUM_REGIONS), "must be");
    71     int* bottom = array.address_mapped_to(fake_heap);
    72     assert((void*)bottom == (void*) array.base(), "must be");
    73     int* end = array.address_mapped_to(fake_heap + REGION_SIZE_IN_WORDS * NUM_REGIONS);
    74     assert((void*)end == (void*)(array.base() + array.length()), "must be");
    75     // The entire array should contain default value elements
    76     for (int* current = bottom; current < end; current++) {
    77       assert(*current == array.default_value(), "must be");
    78     }
    80     // Test setting values in the table
    82     HeapWord* region_start_address = fake_heap + REGION_SIZE_IN_WORDS * (NUM_REGIONS / 2);
    83     HeapWord* region_end_address = fake_heap + (REGION_SIZE_IN_WORDS * (NUM_REGIONS / 2) + REGION_SIZE_IN_WORDS - 1);
    85     // Set/get by address tests: invert some value; first retrieve one
    86     int actual_value = array.get_by_index(NUM_REGIONS / 2);
    87     array.set_by_index(NUM_REGIONS / 2, ~actual_value);
    88     // Get the same value by address, should correspond to the start of the "region"
    89     int value = array.get_by_address(region_start_address);
    90     assert(value == ~actual_value, "must be");
    91     // Get the same value by address, at one HeapWord before the start
    92     value = array.get_by_address(region_start_address - 1);
    93     assert(value == array.default_value(), "must be");
    94     // Get the same value by address, at the end of the "region"
    95     value = array.get_by_address(region_end_address);
    96     assert(value == ~actual_value, "must be");
    97     // Make sure the next value maps to another index
    98     value = array.get_by_address(region_end_address + 1);
    99     assert(value == array.default_value(), "must be");
   101     // Reset the value in the array
   102     array.set_by_address(region_start_address + (region_end_address - region_start_address) / 2, actual_value);
   104     // The entire array should have the default value again
   105     for (int* current = bottom; current < end; current++) {
   106       assert(*current == array.default_value(), "must be");
   107     }
   109     // Set/get by index tests: invert some value
   110     idx_t index = NUM_REGIONS / 2;
   111     actual_value = array.get_by_index(index);
   112     array.set_by_index(index, ~actual_value);
   114     value = array.get_by_index(index);
   115     assert(value == ~actual_value, "must be");
   117     value = array.get_by_index(index - 1);
   118     assert(value == array.default_value(), "must be");
   120     value = array.get_by_index(index + 1);
   121     assert(value == array.default_value(), "must be");
   123     array.set_by_index(0, 0);
   124     value = array.get_by_index(0);
   125     assert(value == 0, "must be");
   127     array.set_by_index(array.length() - 1, 0);
   128     value = array.get_by_index(array.length() - 1);
   129     assert(value == 0, "must be");
   131     array.set_by_index(index, 0);
   133     // The array should have three zeros, and default values otherwise
   134     size_t num_zeros = 0;
   135     for (int* current = bottom; current < end; current++) {
   136       assert(*current == array.default_value() || *current == 0, "must be");
   137       if (*current == 0) {
   138         num_zeros++;
   139       }
   140     }
   141     assert(num_zeros == 3, "must be");
   142   }
   143 };
   145 void TestG1BiasedArray_test() {
   146   TestMappedArray::test_biasedarray();
   147 }
   149 #endif

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