99 * Portions Copyright (c) 2017, PostgreSQL Global Development Group
1010 *
1111 * IDENTIFICATION
12- * src/backend/utils/mmgr/Generation .c
12+ * src/backend/utils/mmgr/generation .c
1313 *
1414 *
1515 *This memory context is based on the assumption that the chunks are freed
2121 *The memory context uses a very simple approach to free space management.
2222 *Instead of a complex global freelist, each block tracks a number
2323 *of allocated and freed chunks. Freed chunks are not reused, and once all
24- *chunkson a block are freed, the whole block is thrown away. When the
25- *chunks allocatedon the same block have similar lifespan, this works
24+ *chunksin a block are freed, the whole block is thrown away. When the
25+ *chunks allocatedin the same block have similar lifespan, this works
2626 *very well and is very cheap.
2727 *
2828 *The current implementation only uses a fixed block size - maybe it should
3838
3939#include "postgres.h"
4040
41+ #include "lib/ilist.h"
4142#include "utils/memdebug.h"
4243#include "utils/memutils.h"
43- #include "lib/ilist.h"
4444
4545
4646#define Generation_BLOCKHDRSZ MAXALIGN(sizeof(GenerationBlock))
4747#define Generation_CHUNKHDRSZ sizeof(GenerationChunk)
4848
49- /* Portion of Generation_CHUNKHDRSZ examined outsideGeneration .c. */
49+ /* Portion of Generation_CHUNKHDRSZ examined outsidegeneration .c. */
5050#define Generation_CHUNK_PUBLIC \
5151(offsetof(GenerationChunk, size) + sizeof(Size))
5252
@@ -65,36 +65,35 @@ typedef struct GenerationChunk GenerationChunk;
6565typedef void * GenerationPointer ;
6666
6767/*
68- * GenerationContext is a simple memory context not reusing allocated chunks, and
69- * freeing blocks once all chunks are freed.
68+ * GenerationContext is a simple memory context not reusing allocated chunks,
69+ *and freeing blocks once all chunks are freed.
7070 */
7171typedef struct GenerationContext
7272{
7373MemoryContextData header ;/* Standard memory-context fields */
7474
75- /*Generationerational context parameters */
75+ /*Generational context parameters */
7676Size blockSize ;/* block size */
7777
7878GenerationBlock * block ;/* current (most recently allocated) block */
7979dlist_head blocks ;/* list of blocks */
80-
8180}GenerationContext ;
8281
8382/*
8483 * GenerationBlock
85- *A GenerationBlock is the unit of memory that is obtained byGeneration .c
84+ *GenerationBlock is the unit of memory that is obtained bygeneration .c
8685 *from malloc(). It contains one or more GenerationChunks, which are
8786 *the units requested by palloc() and freed by pfree(). GenerationChunks
8887 *cannot be returned to malloc() individually, instead pfree()
89- *updatesa free counteron a block and when all chunkson a block
90- *arefreed the whole block is returned to malloc().
88+ *updatesthe free counterof the block and when all chunksin a block
89+ *arefree the whole block is returned to malloc().
9190 *
92- *GenerationBloc is the header data for a block --- the usable space
91+ *GenerationBlock is the header data for a block --- the usable space
9392 *within the block begins at the next alignment boundary.
9493 */
9594struct GenerationBlock
9695{
97- dlist_node node ;/* doubly-linked list */
96+ dlist_node node ;/* doubly-linked listof blocks */
9897int nchunks ;/* number of chunks in the block */
9998int nfree ;/* number of free chunks */
10099char * freeptr ;/* start of free space in this block */
@@ -103,7 +102,7 @@ struct GenerationBlock
103102
104103/*
105104 * GenerationChunk
106- *The prefix of each piece of memory inan GenerationBlock
105+ *The prefix of each piece of memory ina GenerationBlock
107106 */
108107struct GenerationChunk
109108{
@@ -116,9 +115,17 @@ struct GenerationChunk
116115/* when debugging memory usage, also store actual requested size */
117116/* this is zero in a free chunk */
118117Size requested_size ;
119- #endif /* MEMORY_CONTEXT_CHECKING */
118+ #define GENERATIONCHUNK_RAWSIZE (SIZEOF_VOID_P * 2 + SIZEOF_SIZE_T * 2)
119+ #else
120+ #define GENERATIONCHUNK_RAWSIZE (SIZEOF_VOID_P * 2 + SIZEOF_SIZE_T)
121+ #endif /* MEMORY_CONTEXT_CHECKING */
122+
123+ /* ensure proper alignment by adding padding if needed */
124+ #if (GENERATIONCHUNK_RAWSIZE %MAXIMUM_ALIGNOF )!= 0
125+ char padding [MAXIMUM_ALIGNOF - (GENERATIONCHUNK_RAWSIZE %MAXIMUM_ALIGNOF )];
126+ #endif
120127
121- GenerationContext * context ;/* owning context */
128+ GenerationContext * context ;/* owning context */
122129/* there must not be any padding to reach a MAXALIGN boundary here! */
123130};
124131