From 07bd77b95a7846de2b193d1574951436d5783800 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 23 Nov 2017 17:02:15 -0500 Subject: [PATCH] Ensure sizeof(GenerationChunk) is maxaligned. Per buildfarm. Also improve some comments. --- src/backend/utils/mmgr/generation.c | 41 +++++++++++++++++------------ 1 file changed, 24 insertions(+), 17 deletions(-) diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c index cdff20ff81..2ede8e1be9 100644 --- a/src/backend/utils/mmgr/generation.c +++ b/src/backend/utils/mmgr/generation.c @@ -9,7 +9,7 @@ * Portions Copyright (c) 2017, PostgreSQL Global Development Group * * IDENTIFICATION - * src/backend/utils/mmgr/Generation.c + * src/backend/utils/mmgr/generation.c * * * This memory context is based on the assumption that the chunks are freed @@ -21,8 +21,8 @@ * The memory context uses a very simple approach to free space management. * Instead of a complex global freelist, each block tracks a number * of allocated and freed chunks. Freed chunks are not reused, and once all - * chunks on a block are freed, the whole block is thrown away. When the - * chunks allocated on the same block have similar lifespan, this works + * chunks in a block are freed, the whole block is thrown away. When the + * chunks allocated in the same block have similar lifespan, this works * very well and is very cheap. * * The current implementation only uses a fixed block size - maybe it should @@ -38,15 +38,15 @@ #include "postgres.h" +#include "lib/ilist.h" #include "utils/memdebug.h" #include "utils/memutils.h" -#include "lib/ilist.h" #define Generation_BLOCKHDRSZ MAXALIGN(sizeof(GenerationBlock)) #define Generation_CHUNKHDRSZ sizeof(GenerationChunk) -/* Portion of Generation_CHUNKHDRSZ examined outside Generation.c. */ +/* Portion of Generation_CHUNKHDRSZ examined outside generation.c. */ #define Generation_CHUNK_PUBLIC \ (offsetof(GenerationChunk, size) + sizeof(Size)) @@ -65,36 +65,35 @@ typedef struct GenerationChunk GenerationChunk; typedef void *GenerationPointer; /* - * GenerationContext is a simple memory context not reusing allocated chunks, and - * freeing blocks once all chunks are freed. + * GenerationContext is a simple memory context not reusing allocated chunks, + * and freeing blocks once all chunks are freed. */ typedef struct GenerationContext { MemoryContextData header; /* Standard memory-context fields */ - /* Generationerational context parameters */ + /* Generational context parameters */ Size blockSize; /* block size */ GenerationBlock *block; /* current (most recently allocated) block */ dlist_head blocks; /* list of blocks */ - } GenerationContext; /* * GenerationBlock - * A GenerationBlock is the unit of memory that is obtained by Generation.c + * GenerationBlock is the unit of memory that is obtained by generation.c * from malloc(). It contains one or more GenerationChunks, which are * the units requested by palloc() and freed by pfree(). GenerationChunks * cannot be returned to malloc() individually, instead pfree() - * updates a free counter on a block and when all chunks on a block - * are freed the whole block is returned to malloc(). + * updates the free counter of the block and when all chunks in a block + * are free the whole block is returned to malloc(). * - * GenerationBloc is the header data for a block --- the usable space + * GenerationBlock is the header data for a block --- the usable space * within the block begins at the next alignment boundary. */ struct GenerationBlock { - dlist_node node; /* doubly-linked list */ + dlist_node node; /* doubly-linked list of blocks */ int nchunks; /* number of chunks in the block */ int nfree; /* number of free chunks */ char *freeptr; /* start of free space in this block */ @@ -103,7 +102,7 @@ struct GenerationBlock /* * GenerationChunk - * The prefix of each piece of memory in an GenerationBlock + * The prefix of each piece of memory in a GenerationBlock */ struct GenerationChunk { @@ -116,9 +115,17 @@ struct GenerationChunk /* when debugging memory usage, also store actual requested size */ /* this is zero in a free chunk */ Size requested_size; -#endif /* MEMORY_CONTEXT_CHECKING */ +#define GENERATIONCHUNK_RAWSIZE (SIZEOF_VOID_P * 2 + SIZEOF_SIZE_T * 2) +#else +#define GENERATIONCHUNK_RAWSIZE (SIZEOF_VOID_P * 2 + SIZEOF_SIZE_T) +#endif /* MEMORY_CONTEXT_CHECKING */ + + /* ensure proper alignment by adding padding if needed */ +#if (GENERATIONCHUNK_RAWSIZE % MAXIMUM_ALIGNOF) != 0 + char padding[MAXIMUM_ALIGNOF - (GENERATIONCHUNK_RAWSIZE % MAXIMUM_ALIGNOF)]; +#endif - GenerationContext *context; /* owning context */ + GenerationContext *context; /* owning context */ /* there must not be any padding to reach a MAXALIGN boundary here! */ }; -- 2.40.0