memutils.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * memutils.h
 *    This file contains declarations for memory allocation utility
 *    functions.  These are functions that are not quite widely used
 *    enough to justify going in utils/palloc.h, but are still part
 *    of the API of the memory management subsystem.
 *
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/utils/memutils.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef MEMUTILS_H
#define MEMUTILS_H

#include "nodes/memnodes.h"


/*
 * MaxAllocSize, MaxAllocHugeSize
 *      Quasi-arbitrary limits on size of allocations.
 *
 * Note:
 *      There is no guarantee that smaller allocations will succeed, but
 *      larger requests will be summarily denied.
 *
 * palloc() enforces MaxAllocSize, chosen to correspond to the limiting size
 * of varlena objects under TOAST.  See VARSIZE_4B() and related macros in
 * postgres.h.  Many datatypes assume that any allocatable size can be
 * represented in a varlena header.  This limit also permits a caller to use
 * an "int" variable for an index into or length of an allocation.  Callers
 * careful to avoid these hazards can access the higher limit with
 * MemoryContextAllocHuge().  Both limits permit code to assume that it may
 * compute twice an allocation's size without overflow.
 */
#define MaxAllocSize    ((Size) 0x3fffffff) /* 1 gigabyte - 1 */

#define AllocSizeIsValid(size)  ((Size) (size) <= MaxAllocSize)

#define MaxAllocHugeSize    ((Size) -1 >> 1)    /* SIZE_MAX / 2 */

#define AllocHugeSizeIsValid(size)  ((Size) (size) <= MaxAllocHugeSize)


/*
 * Standard top-level memory contexts.
 *
 * Only TopMemoryContext and ErrorContext are initialized by
 * MemoryContextInit() itself.
 */
extern PGDLLIMPORT MemoryContext TopMemoryContext;
extern PGDLLIMPORT MemoryContext ErrorContext;
extern PGDLLIMPORT MemoryContext PostmasterContext;
extern PGDLLIMPORT MemoryContext CacheMemoryContext;
extern PGDLLIMPORT MemoryContext MessageContext;
extern PGDLLIMPORT MemoryContext TopTransactionContext;
extern PGDLLIMPORT MemoryContext CurTransactionContext;

/* This is a transient link to the active portal's memory context: */
extern PGDLLIMPORT MemoryContext PortalContext;

/* Backwards compatibility macro */
#define MemoryContextResetAndDeleteChildren(ctx) MemoryContextReset(ctx)


/*
 * Memory-context-type-independent functions in mcxt.c
 */
extern void MemoryContextInit(void);
extern void MemoryContextReset(MemoryContext context);
extern void MemoryContextDelete(MemoryContext context);
extern void MemoryContextResetOnly(MemoryContext context);
extern void MemoryContextResetChildren(MemoryContext context);
extern void MemoryContextDeleteChildren(MemoryContext context);
extern void MemoryContextSetParent(MemoryContext context,
                       MemoryContext new_parent);
extern Size GetMemoryChunkSpace(void *pointer);
extern MemoryContext MemoryContextGetParent(MemoryContext context);
extern bool MemoryContextIsEmpty(MemoryContext context);
extern void MemoryContextStats(MemoryContext context);
extern void MemoryContextStatsDetail(MemoryContext context, int max_children);
extern void MemoryContextAllowInCriticalSection(MemoryContext context,
                                    bool allow);

#ifdef MEMORY_CONTEXT_CHECKING
extern void MemoryContextCheck(MemoryContext context);
#endif
extern bool MemoryContextContains(MemoryContext context, void *pointer);

/*
 * GetMemoryChunkContext
 *      Given a currently-allocated chunk, determine the context
 *      it belongs to.
 *
 * All chunks allocated by any memory context manager are required to be
 * preceded by the corresponding MemoryContext stored, without padding, in the
 * preceding sizeof(void*) bytes.  A currently-allocated chunk must contain a
 * backpointer to its owning context.  The backpointer is used by pfree() and
 * repalloc() to find the context to call.
 */
#ifndef FRONTEND
static inline MemoryContext
GetMemoryChunkContext(void *pointer)
{
    MemoryContext context;

    /*
     * Try to detect bogus pointers handed to us, poorly though we can.
     * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an
     * allocated chunk.
     */
    Assert(pointer != NULL);
    Assert(pointer == (void *) MAXALIGN(pointer));

    /*
     * OK, it's probably safe to look at the context.
     */
    context = *(MemoryContext *) (((char *) pointer) - sizeof(void *));

    AssertArg(MemoryContextIsValid(context));

    return context;
}
#endif

/*
 * This routine handles the context-type-independent part of memory
 * context creation.  It's intended to be called from context-type-
 * specific creation routines, and noplace else.
 */
extern MemoryContext MemoryContextCreate(NodeTag tag, Size size,
                    MemoryContextMethods *methods,
                    MemoryContext parent,
                    const char *name);


/*
 * Memory-context-type-specific functions
 */

/* aset.c */
extern MemoryContext AllocSetContextCreate(MemoryContext parent,
                      const char *name,
                      Size minContextSize,
                      Size initBlockSize,
                      Size maxBlockSize);

/* slab.c */
extern MemoryContext SlabContextCreate(MemoryContext parent,
                  const char *name,
                  Size blockSize,
                  Size chunkSize);

/*
 * Recommended default alloc parameters, suitable for "ordinary" contexts
 * that might hold quite a lot of data.
 */
#define ALLOCSET_DEFAULT_MINSIZE   0
#define ALLOCSET_DEFAULT_INITSIZE  (8 * 1024)
#define ALLOCSET_DEFAULT_MAXSIZE   (8 * 1024 * 1024)
#define ALLOCSET_DEFAULT_SIZES \
    ALLOCSET_DEFAULT_MINSIZE, ALLOCSET_DEFAULT_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE

/*
 * Recommended alloc parameters for "small" contexts that are never expected
 * to contain much data (for example, a context to contain a query plan).
 */
#define ALLOCSET_SMALL_MINSIZE   0
#define ALLOCSET_SMALL_INITSIZE  (1 * 1024)
#define ALLOCSET_SMALL_MAXSIZE   (8 * 1024)
#define ALLOCSET_SMALL_SIZES \
    ALLOCSET_SMALL_MINSIZE, ALLOCSET_SMALL_INITSIZE, ALLOCSET_SMALL_MAXSIZE

/*
 * Recommended alloc parameters for contexts that should start out small,
 * but might sometimes grow big.
 */
#define ALLOCSET_START_SMALL_SIZES \
    ALLOCSET_SMALL_MINSIZE, ALLOCSET_SMALL_INITSIZE, ALLOCSET_DEFAULT_MAXSIZE


/*
 * Threshold above which a request in an AllocSet context is certain to be
 * allocated separately (and thereby have constant allocation overhead).
 * Few callers should be interested in this, but tuplesort/tuplestore need
 * to know it.
 */
#define ALLOCSET_SEPARATE_THRESHOLD  8192

#define SLAB_DEFAULT_BLOCK_SIZE     (8 * 1024)
#define SLAB_LARGE_BLOCK_SIZE       (8 * 1024 * 1024)

#endif                          /* MEMUTILS_H */