PostgreSQL Source Code  git master
 All Data Structures Namespaces Files Functions Variables Typedefs Enumerations Enumerator Macros
memutils.h
Go to the documentation of this file.
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) -1 >> 1) /* 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  */
62 
63 /* This is a transient link to the active portal's memory context: */
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);
83 extern bool MemoryContextIsEmpty(MemoryContext context);
84 extern void MemoryContextStats(MemoryContext context);
85 extern void MemoryContextStatsDetail(MemoryContext context, int max_children);
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
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 
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  */
136  MemoryContextMethods *methods,
137  MemoryContext parent,
138  const char *name);
139 
140 
141 /*
142  * Memory-context-type-specific functions
143  */
144 
145 /* aset.c */
147  const char *name,
148  Size minContextSize,
149  Size initBlockSize,
150  Size maxBlockSize);
151 
152 /* slab.c */
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 */
void MemoryContextDelete(MemoryContext context)
Definition: mcxt.c:200
PGDLLIMPORT MemoryContext CacheMemoryContext
Definition: mcxt.c:46
bool MemoryContextIsEmpty(MemoryContext context)
Definition: mcxt.c:415
void MemoryContextAllowInCriticalSection(MemoryContext context, bool allow)
Definition: mcxt.c:374
MemoryContext SlabContextCreate(MemoryContext parent, const char *name, Size blockSize, Size chunkSize)
Definition: slab.c:183
void MemoryContextDeleteChildren(MemoryContext context)
Definition: mcxt.c:236
void MemoryContextResetOnly(MemoryContext context)
Definition: mcxt.c:154
void MemoryContextReset(MemoryContext context)
Definition: mcxt.c:135
PGDLLIMPORT MemoryContext PortalContext
Definition: mcxt.c:52
PGDLLIMPORT MemoryContext PostmasterContext
Definition: mcxt.c:45
NodeTag
Definition: nodes.h:26
#define PGDLLIMPORT
Definition: c.h:1063
bool MemoryContextContains(MemoryContext context, void *pointer)
Definition: mcxt.c:567
MemoryContext AllocSetContextCreate(MemoryContext parent, const char *name, Size minContextSize, Size initBlockSize, Size maxBlockSize)
Definition: aset.c:322
void MemoryContextStats(MemoryContext context)
Definition: mcxt.c:438
PGDLLIMPORT MemoryContext TopTransactionContext
Definition: mcxt.c:48
PGDLLIMPORT MemoryContext MessageContext
Definition: mcxt.c:47
MemoryContext MemoryContextGetParent(MemoryContext context)
Definition: mcxt.c:403
Size GetMemoryChunkSpace(void *pointer)
Definition: mcxt.c:390
void MemoryContextResetChildren(MemoryContext context)
Definition: mcxt.c:176
#define AssertArg(condition)
Definition: c.h:677
PGDLLIMPORT MemoryContext CurTransactionContext
Definition: mcxt.c:49
void MemoryContextStatsDetail(MemoryContext context, int max_children)
Definition: mcxt.c:450
#define MemoryContextIsValid(context)
Definition: memnodes.h:97
#define NULL
Definition: c.h:229
#define Assert(condition)
Definition: c.h:675
void MemoryContextSetParent(MemoryContext context, MemoryContext new_parent)
Definition: mcxt.c:317
size_t Size
Definition: c.h:356
#define MAXALIGN(LEN)
Definition: c.h:588
const char * name
Definition: encode.c:521
PGDLLIMPORT MemoryContext TopMemoryContext
Definition: mcxt.c:43
PGDLLIMPORT MemoryContext ErrorContext
Definition: mcxt.c:44
void MemoryContextInit(void)
Definition: mcxt.c:89
MemoryContext MemoryContextCreate(NodeTag tag, Size size, MemoryContextMethods *methods, MemoryContext parent, const char *name)
Definition: mcxt.c:640
static MemoryContext GetMemoryChunkContext(void *pointer)
Definition: memutils.h:107