1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
|
/**
* Copyright (C) 2014 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/util/concurrency/mutex.h"
namespace mongo {
class MmapV1RecordHeader;
/**
* Used to implement likelyInPhysicalMemory() for the MMAP v1 storage engine. Since
* MMAP v1 holds exclusive collection-level locks, it should yield the locks during a
* page fault. The RecordAccessTracker is used to guess at which records are in memory,
* so that a yield can be requested unless we're sure that the record has been
* recently accessed.
*/
class RecordAccessTracker {
MONGO_DISALLOW_COPYING(RecordAccessTracker);
public:
RecordAccessTracker();
enum Constants {
SliceSize = 1024,
MaxChain = 20, // intentionally very low
NumSlices = 10,
RotateTimeSecs = 90,
BigHashSize = 128
};
/**
* Informs this record access tracker that 'record' has been accessed.
*/
void markAccessed(const void* record);
/**
* @return whether or not 'record' has been marked as accessed recently. A return value
* of true means that 'record' is likely in physical memory.
*
* Also has the side effect of marking 'record' as accessed.
*/
bool checkAccessedAndMark(const void* record);
/**
* Clears out any history of record accesses.
*/
void reset();
//
// For testing.
//
/**
* The accessedRecently() implementation falls back to making a system call if it
* appears that the record is not in physical memory. Use this method to disable
* the fallback for testing.
*/
void disableSystemBlockInMemCheck();
private:
enum State { In, Out, Unk };
struct Entry {
size_t region;
unsigned long long value;
};
/**
* simple hash map for region -> status
* this constitutes a single region of time
* it does chaining, but very short chains
*/
class Slice {
public:
Slice();
void reset();
State get(int regionHash, size_t region, short offset);
/**
* @return true if added, false if full
*/
bool put(int regionHash, size_t region, short offset);
time_t lastReset() const;
private:
Entry* _get(int start, size_t region, bool add);
Entry _data[SliceSize];
time_t _lastReset;
};
/**
* this contains many slices of times
* the idea you put mem status in the current time slice
* and then after a certain period of time, it rolls off so we check again
*/
class Rolling {
public:
Rolling();
/**
* After this call, we assume the page is in RAM.
*
* @param doHalf if this is a known good access, want to put in first half.
*
* @return whether we know the page is in RAM
*/
bool access(size_t region, short offset, bool doHalf);
private:
void _rotate();
int _curSlice;
long long _lastRotate;
Slice _slices[NumSlices];
SimpleMutex _lock;
};
// Should this record tracker fallback to making a system call?
bool _blockSupported;
// An array of Rolling instances for tracking record accesses.
std::unique_ptr<Rolling[]> _rollingTable;
};
} // namespace
|
