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postgres/src/include/utils/memutils_internal.h
David Rowley 743112a2e9 Adjust memory allocation functions to allow sibling calls 
Many modern compilers are able to optimize function calls to functions
where the parameters of the called function match a leading subset of
the calling function's parameters.  If there are no instructions in the
calling function after the function is called, then the compiler is free
to avoid any stack frame setup and implement the function call as a
"jmp" rather than a "call".  This is called sibling call optimization.

Here we adjust the memory allocation functions in mcxt.c to allow this
optimization.  This requires moving some responsibility into the memory
context implementations themselves.  It's now the responsibility of the
MemoryContext to check for malloc failures.  This is good as it both
allows the sibling call optimization, but also because most small and
medium allocations won't call malloc and just allocate memory to an
existing block.  That can't fail, so checking for NULLs in that case
isn't required.

Also, traditionally it's been the responsibility of palloc and the other
allocation functions in mcxt.c to check for invalid allocation size
requests.  Here we also move the responsibility of checking that into the
MemoryContext.  This isn't to allow the sibling call optimization, but
more because most of our allocators handle large allocations separately
and we can just add the size check when doing large allocations.  We no
longer check this for non-large allocations at all.

To make checking the allocation request sizes and ERROR handling easier,
add some helper functions to mcxt.c for the allocators to use.

Author: Andres Freund
Reviewed-by: David Rowley
Discussion: https://postgr.es/m/20210719195950.gavgs6ujzmjfaiig@alap3.anarazel.de
2024-02-27 16:39:42 +13:00

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/*-------------------------------------------------------------------------
*
* memutils_internal.h
* This file contains declarations for memory allocation utility
* functions for internal use.
*
*
* Portions Copyright (c) 2022-2024, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/utils/memutils_internal.h
*
*-------------------------------------------------------------------------
*/
#ifndef MEMUTILS_INTERNAL_H
#define MEMUTILS_INTERNAL_H
#include "utils/memutils.h"
/* These functions implement the MemoryContext API for AllocSet context. */
extern void *AllocSetAlloc(MemoryContext context, Size size, int flags);
extern void AllocSetFree(void *pointer);
extern void *AllocSetRealloc(void *pointer, Size size, int flags);
extern void AllocSetReset(MemoryContext context);
extern void AllocSetDelete(MemoryContext context);
extern MemoryContext AllocSetGetChunkContext(void *pointer);
extern Size AllocSetGetChunkSpace(void *pointer);
extern bool AllocSetIsEmpty(MemoryContext context);
extern void AllocSetStats(MemoryContext context,
MemoryStatsPrintFunc printfunc, void *passthru,
MemoryContextCounters *totals,
bool print_to_stderr);
#ifdef MEMORY_CONTEXT_CHECKING
extern void AllocSetCheck(MemoryContext context);
#endif
/* These functions implement the MemoryContext API for Generation context. */
extern void *GenerationAlloc(MemoryContext context, Size size, int flags);
extern void GenerationFree(void *pointer);
extern void *GenerationRealloc(void *pointer, Size size, int flags);
extern void GenerationReset(MemoryContext context);
extern void GenerationDelete(MemoryContext context);
extern MemoryContext GenerationGetChunkContext(void *pointer);
extern Size GenerationGetChunkSpace(void *pointer);
extern bool GenerationIsEmpty(MemoryContext context);
extern void GenerationStats(MemoryContext context,
MemoryStatsPrintFunc printfunc, void *passthru,
MemoryContextCounters *totals,
bool print_to_stderr);
#ifdef MEMORY_CONTEXT_CHECKING
extern void GenerationCheck(MemoryContext context);
#endif
/* These functions implement the MemoryContext API for Slab context. */
extern void *SlabAlloc(MemoryContext context, Size size, int flags);
extern void SlabFree(void *pointer);
extern void *SlabRealloc(void *pointer, Size size, int flags);
extern void SlabReset(MemoryContext context);
extern void SlabDelete(MemoryContext context);
extern MemoryContext SlabGetChunkContext(void *pointer);
extern Size SlabGetChunkSpace(void *pointer);
extern bool SlabIsEmpty(MemoryContext context);
extern void SlabStats(MemoryContext context,
MemoryStatsPrintFunc printfunc, void *passthru,
MemoryContextCounters *totals,
bool print_to_stderr);
#ifdef MEMORY_CONTEXT_CHECKING
extern void SlabCheck(MemoryContext context);
#endif
/*
* These functions support the implementation of palloc_aligned() and are not
* part of a fully-fledged MemoryContext type.
*/
extern void AlignedAllocFree(void *pointer);
extern void *AlignedAllocRealloc(void *pointer, Size size, int flags);
extern MemoryContext AlignedAllocGetChunkContext(void *pointer);
extern Size AlignedAllocGetChunkSpace(void *pointer);
/*
* How many extra bytes do we need to request in order to ensure that we can
* align a pointer to 'alignto'. Since palloc'd pointers are already aligned
* to MAXIMUM_ALIGNOF we can subtract that amount. We also need to make sure
* there is enough space for the redirection MemoryChunk.
*/
#define PallocAlignedExtraBytes(alignto) \
((alignto) + (sizeof(MemoryChunk) - MAXIMUM_ALIGNOF))
/*
* MemoryContextMethodID
* A unique identifier for each MemoryContext implementation which
* indicates the index into the mcxt_methods[] array. See mcxt.c.
*
* For robust error detection, ensure that MemoryContextMethodID has a value
* for each possible bit-pattern of MEMORY_CONTEXT_METHODID_MASK, and make
* dummy entries for unused IDs in the mcxt_methods[] array. We also try
* to avoid using bit-patterns as valid IDs if they are likely to occur in
* garbage data, or if they could falsely match on chunks that are really from
* malloc not palloc. (We can't tell that for most malloc implementations,
* but it happens that glibc stores flag bits in the same place where we put
* the MemoryContextMethodID, so the possible values are predictable for it.)
*/
typedef enum MemoryContextMethodID
{
MCTX_UNUSED1_ID, /* 000 occurs in never-used memory */
MCTX_UNUSED2_ID, /* glibc malloc'd chunks usually match 001 */
MCTX_UNUSED3_ID, /* glibc malloc'd chunks > 128kB match 010 */
MCTX_ASET_ID,
MCTX_GENERATION_ID,
MCTX_SLAB_ID,
MCTX_ALIGNED_REDIRECT_ID,
MCTX_UNUSED4_ID, /* 111 occurs in wipe_mem'd memory */
} MemoryContextMethodID;
/*
* The number of bits that 8-byte memory chunk headers can use to encode the
* MemoryContextMethodID.
*/
#define MEMORY_CONTEXT_METHODID_BITS 3
#define MEMORY_CONTEXT_METHODID_MASK \
((((uint64) 1) << MEMORY_CONTEXT_METHODID_BITS) - 1)
/*
* 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 void MemoryContextCreate(MemoryContext node,
NodeTag tag,
MemoryContextMethodID method_id,
MemoryContext parent,
const char *name);
extern void *MemoryContextAllocationFailure(MemoryContext context, Size size,
int flags);
extern void MemoryContextSizeFailure(MemoryContext context, Size size,
int flags) pg_attribute_noreturn();
static inline void
MemoryContextCheckSize(MemoryContext context, Size size, int flags)
{
if (unlikely(!AllocSizeIsValid(size)))
{
if (!(flags & MCXT_ALLOC_HUGE) || !AllocHugeSizeIsValid(size))
MemoryContextSizeFailure(context, size, flags);
}
}
#endif /* MEMUTILS_INTERNAL_H */
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