1 /*

     2  * Copyright (c) 2019, 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 #include "precompiled.hpp"

    25 #include "gc/z/zCPU.inline.hpp"

    26 #include "gc/z/zGlobals.hpp"

    27 #include "gc/z/zHeuristics.hpp"

    28 #include "gc/z/zUtils.inline.hpp"

    29 #include "logging/log.hpp"

    30 #include "runtime/globals.hpp"

    31 #include "runtime/os.hpp"

    32 

    33 void ZHeuristics::set_medium_page_size() {

    34   // Set ZPageSizeMedium so that a medium page occupies at most 3.125% of the

    35   // max heap size. ZPageSizeMedium is initially set to 0, which means medium

    36   // pages are effectively disabled. It is adjusted only if ZPageSizeMedium

    37   // becomes larger than ZPageSizeSmall.

    38   const size_t min = ZGranuleSize;

    39   const size_t max = ZGranuleSize * 16;

    40   const size_t unclamped = MaxHeapSize * 0.03125;

    41   const size_t clamped = MIN2(MAX2(min, unclamped), max);

    42   const size_t size = ZUtils::round_down_power_of_2(clamped);

    43 

    44   if (size > ZPageSizeSmall) {

    45     // Enable medium pages

    46     ZPageSizeMedium             = size;

    47     ZPageSizeMediumShift        = log2_intptr(ZPageSizeMedium);

    48     ZObjectSizeLimitMedium      = ZPageSizeMedium / 8;

    49     ZObjectAlignmentMediumShift = ZPageSizeMediumShift - 13;

    50     ZObjectAlignmentMedium      = 1 << ZObjectAlignmentMediumShift;

    51 

    52     log_info(gc, init)("Medium Page Size: " SIZE_FORMAT "M", ZPageSizeMedium / M);

    53   } else {

    54     log_info(gc, init)("Medium Page Size: N/A");

    55   }

    56 }

    57 

    58 bool ZHeuristics::use_per_cpu_shared_small_pages() {

    59   // Use per-CPU shared small pages only if these pages occupy at most 3.125%

    60   // of the max heap size. Otherwise fall back to using a single shared small

    61   // page. This is useful when using small heaps on large machines.

    62   const size_t per_cpu_share = (MaxHeapSize * 0.03125) / ZCPU::count();

    63   return per_cpu_share >= ZPageSizeSmall;

    64 }