1 /*

     2  * Copyright (c) 2012, 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  */

    24 

    25 #include "precompiled.hpp"

    26 #include "memory/allocation.hpp"

    27 #include "memory/metablock.hpp"

    28 #include "utilities/copy.hpp"

    29 #include "utilities/debug.hpp"

    30 

    31 // Blocks of space for metadata are allocated out of Metachunks.

    32 //

    33 // Metachunk are allocated out of MetadataVirtualspaces and once

    34 // allocated there is no explicit link between a Metachunk and

    35 // the MetadataVirtualspaces from which it was allocated.

    36 //

    37 // Each SpaceManager maintains a

    38 // list of the chunks it is using and the current chunk.  The current

    39 // chunk is the chunk from which allocations are done.  Space freed in

    40 // a chunk is placed on the free list of blocks (BlockFreelist) and

    41 // reused from there.

    42 //

    43 // Future modification

    44 //

    45 // The Metachunk can conceivable be replaced by the Chunk in

    46 // allocation.hpp.  Note that the latter Chunk is the space for

    47 // allocation (allocations from the chunk are out of the space in

    48 // the Chunk after the header for the Chunk) where as Metachunks

    49 // point to space in a VirtualSpace.  To replace Metachunks with

    50 // Chunks, change Chunks so that they can be allocated out of a VirtualSpace.

    51 size_t Metablock::_min_block_byte_size = sizeof(Metablock);

    52 

    53 #ifdef ASSERT

    54 size_t Metablock::_overhead =

    55   Chunk::aligned_overhead_size(sizeof(Metablock)) / BytesPerWord;

    56 #else

    57 size_t Metablock::_overhead = 0;

    58 #endif

    59 

    60 // New blocks returned by the Metaspace are zero initialized.

    61 // We should fix the constructors to not assume this instead.

    62 Metablock* Metablock::initialize(MetaWord* p, size_t word_size) {

    63   if (p == NULL) {

    64     return NULL;

    65   }

    66 

    67   Metablock* result = (Metablock*) p;

    68 

    69   // Clear the memory

    70   Copy::fill_to_aligned_words((HeapWord*)result, word_size);

    71 #ifdef ASSERT

    72   result->set_word_size(word_size);

    73 #endif

    74   return result;

    75 }