From 07bd77b95a7846de2b193d1574951436d5783800 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
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 cdff20ff815..2ede8e1be93 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! */
};
--
GitLab