1 /*-------------------------------------------------------------------------
2 *
3 * memutils.h
4 * This file contains declarations for memory allocation utility
5 * functions. These are functions that are not quite widely used
6 * enough to justify going in utils/palloc.h, but are still part
7 * of the API of the memory management subsystem.
8 *
9 *
10 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
11 * Portions Copyright (c) 1994, Regents of the University of California
12 *
13 * src/include/utils/memutils.h
14 *
15 *-------------------------------------------------------------------------
16 */
17 #ifndef MEMUTILS_H
18 #define MEMUTILS_H
19
20 #include "nodes/memnodes.h"
21
22
23 /*
24 * MaxAllocSize, MaxAllocHugeSize
25 * Quasi-arbitrary limits on size of allocations.
26 *
27 * Note:
28 * There is no guarantee that smaller allocations will succeed, but
29 * larger requests will be summarily denied.
30 *
31 * palloc() enforces MaxAllocSize, chosen to correspond to the limiting size
32 * of varlena objects under TOAST. See VARSIZE_4B() and related macros in
33 * postgres.h. Many datatypes assume that any allocatable size can be
34 * represented in a varlena header. This limit also permits a caller to use
35 * an "int" variable for an index into or length of an allocation. Callers
36 * careful to avoid these hazards can access the higher limit with
37 * MemoryContextAllocHuge(). Both limits permit code to assume that it may
38 * compute twice an allocation's size without overflow.
39 */
40 #define MaxAllocSize ((Size) 0x3fffffff) /* 1 gigabyte - 1 */
41
42 #define AllocSizeIsValid(size) ((Size) (size) <= MaxAllocSize)
43
44 #define MaxAllocHugeSize (SIZE_MAX / 2)
45
46 #define AllocHugeSizeIsValid(size) ((Size) (size) <= MaxAllocHugeSize)
47
48
49 /*
50 * Standard top-level memory contexts.
51 *
52 * Only TopMemoryContext and ErrorContext are initialized by
53 * MemoryContextInit() itself.
54 */
55 extern PGDLLIMPORT MemoryContext TopMemoryContext;
56 extern PGDLLIMPORT MemoryContext ErrorContext;
57 extern PGDLLIMPORT MemoryContext PostmasterContext;
58 extern PGDLLIMPORT MemoryContext CacheMemoryContext;
59 extern PGDLLIMPORT MemoryContext MessageContext;
60 extern PGDLLIMPORT MemoryContext TopTransactionContext;
61 extern PGDLLIMPORT MemoryContext CurTransactionContext;
62
63 /* This is a transient link to the active portal's memory context: */
64 extern PGDLLIMPORT MemoryContext PortalContext;
65
66 /* Backwards compatibility macro */
67 #define MemoryContextResetAndDeleteChildren(ctx) MemoryContextReset(ctx)
68
69
70 /*
71 * Memory-context-type-independent functions in mcxt.c
72 */
73 extern void MemoryContextInit(void);
74 extern void MemoryContextReset(MemoryContext context);
75 extern void MemoryContextDelete(MemoryContext context);
76 extern void MemoryContextResetOnly(MemoryContext context);
77 extern void MemoryContextResetChildren(MemoryContext context);
78 extern void MemoryContextDeleteChildren(MemoryContext context);
79 extern void MemoryContextSetParent(MemoryContext context,
80 MemoryContext new_parent);
81 extern Size GetMemoryChunkSpace(void *pointer);
82 extern MemoryContext MemoryContextGetParent(MemoryContext context);
83 extern bool MemoryContextIsEmpty(MemoryContext context);
84 extern void MemoryContextStats(MemoryContext context);
85 extern void MemoryContextStatsDetail(MemoryContext context, int max_children);
86 extern void MemoryContextAllowInCriticalSection(MemoryContext context,
87 bool allow);
88
89 #ifdef MEMORY_CONTEXT_CHECKING
90 extern void MemoryContextCheck(MemoryContext context);
91 #endif
92 extern bool MemoryContextContains(MemoryContext context, void *pointer);
93
94 /*
95 * GetMemoryChunkContext
96 * Given a currently-allocated chunk, determine the context
97 * it belongs to.
98 *
99 * All chunks allocated by any memory context manager are required to be
100 * preceded by the corresponding MemoryContext stored, without padding, in the
101 * preceding sizeof(void*) bytes. A currently-allocated chunk must contain a
102 * backpointer to its owning context. The backpointer is used by pfree() and
103 * repalloc() to find the context to call.
104 */
105 #ifndef FRONTEND
106 static inline MemoryContext
GetMemoryChunkContext(void * pointer)107 GetMemoryChunkContext(void *pointer)
108 {
109 MemoryContext context;
110
111 /*
112 * Try to detect bogus pointers handed to us, poorly though we can.
113 * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an
114 * allocated chunk.
115 */
116 Assert(pointer != NULL);
117 Assert(pointer == (void *) MAXALIGN(pointer));
118
119 /*
120 * OK, it's probably safe to look at the context.
121 */
122 context = *(MemoryContext *) (((char *) pointer) - sizeof(void *));
123
124 AssertArg(MemoryContextIsValid(context));
125
126 return context;
127 }
128 #endif
129
130 /*
131 * This routine handles the context-type-independent part of memory
132 * context creation. It's intended to be called from context-type-
133 * specific creation routines, and noplace else.
134 */
135 extern MemoryContext MemoryContextCreate(NodeTag tag, Size size,
136 MemoryContextMethods *methods,
137 MemoryContext parent,
138 const char *name);
139
140
141 /*
142 * Memory-context-type-specific functions
143 */
144
145 /* aset.c */
146 extern MemoryContext AllocSetContextCreate(MemoryContext parent,
147 const char *name,
148 Size minContextSize,
149 Size initBlockSize,
150 Size maxBlockSize);
151
152 /* slab.c */
153 extern MemoryContext SlabContextCreate(MemoryContext parent,
154 const char *name,
155 Size blockSize,
156 Size chunkSize);
157
158 /*
159 * Recommended default alloc parameters, suitable for "ordinary" contexts
160 * that might hold quite a lot of data.
161 */
162 #define ALLOCSET_DEFAULT_MINSIZE 0
163 #define ALLOCSET_DEFAULT_INITSIZE (8 * 1024)
164 #define ALLOCSET_DEFAULT_MAXSIZE (8 * 1024 * 1024)
165 #define ALLOCSET_DEFAULT_SIZES \
166 ALLOCSET_DEFAULT_MINSIZE, ALLOCSET_DEFAULT_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE
167
168 /*
169 * Recommended alloc parameters for "small" contexts that are never expected
170 * to contain much data (for example, a context to contain a query plan).
171 */
172 #define ALLOCSET_SMALL_MINSIZE 0
173 #define ALLOCSET_SMALL_INITSIZE (1 * 1024)
174 #define ALLOCSET_SMALL_MAXSIZE (8 * 1024)
175 #define ALLOCSET_SMALL_SIZES \
176 ALLOCSET_SMALL_MINSIZE, ALLOCSET_SMALL_INITSIZE, ALLOCSET_SMALL_MAXSIZE
177
178 /*
179 * Recommended alloc parameters for contexts that should start out small,
180 * but might sometimes grow big.
181 */
182 #define ALLOCSET_START_SMALL_SIZES \
183 ALLOCSET_SMALL_MINSIZE, ALLOCSET_SMALL_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE
184
185
186 /*
187 * Threshold above which a request in an AllocSet context is certain to be
188 * allocated separately (and thereby have constant allocation overhead).
189 * Few callers should be interested in this, but tuplesort/tuplestore need
190 * to know it.
191 */
192 #define ALLOCSET_SEPARATE_THRESHOLD 8192
193
194 #define SLAB_DEFAULT_BLOCK_SIZE (8 * 1024)
195 #define SLAB_LARGE_BLOCK_SIZE (8 * 1024 * 1024)
196
197 #endif /* MEMUTILS_H */
198