Ensure sizeof(GenerationChunk) is maxaligned.

Per buildfarm.

Also improve some comments.

diff --git a/src/backend/utils/mmgr/generation.c b/src/backend/utils/mmgr/generation.c
index cdff20ff81594b34cc41d1d22770d90d959f5550..2ede8e1be93ff9392e2fdc9e19ca64b014202ec6 100644 (file)
--- 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! */
 };