Specialize MemoryContextMemAllocated().

An AllocSet doubles the size of allocated blocks (up to maxBlockSize),
which means that the current block can represent half of the total
allocated space for the memory context. But the free space in the
current block may never have been touched, so don't count the
untouched memory as allocated for the purposes of
MemoryContextMemAllocated().

Discussion: https://postgr.es/m/ec63d70b668818255486a83ffadc3aec492c1f57.camel@j-davis.com

src/backend/utils/mmgr/aset.c

@@ -132,6 +132,7 @@ typedef struct AllocSetContext
 	Size		maxBlockSize;	/* maximum block size */
 	Size		nextBlockSize;	/* next block size to allocate */
 	Size		allocChunkLimit;	/* effective chunk size limit */
+	Size		memAllocated;	/* track memory allocated for this context */
 	AllocBlock	keeper;			/* keep this block over resets */
 	/* freelist this context could be put in, or -1 if not a candidate: */
 	int			freeListIndex;	/* index in context_freelists[], or -1 */
@@ -272,6 +273,7 @@ static void *AllocSetRealloc(MemoryContext context, void *pointer, Size size);
 static void AllocSetReset(MemoryContext context);
 static void AllocSetDelete(MemoryContext context);
 static Size AllocSetGetChunkSpace(MemoryContext context, void *pointer);
+static Size AllocSetMemAllocated(MemoryContext context);
 static bool AllocSetIsEmpty(MemoryContext context);
 static void AllocSetStats(MemoryContext context,
 						  MemoryStatsPrintFunc printfunc, void *passthru,
@@ -291,6 +293,7 @@ static const MemoryContextMethods AllocSetMethods = {
 	AllocSetReset,
 	AllocSetDelete,
 	AllocSetGetChunkSpace,
+	AllocSetMemAllocated,
 	AllocSetIsEmpty,
 	AllocSetStats
 #ifdef MEMORY_CONTEXT_CHECKING
@@ -464,8 +467,7 @@ AllocSetContextCreateInternal(MemoryContext parent,
 								parent,
 								name);
 
-			((MemoryContext) set)->mem_allocated =
-				set->keeper->endptr - ((char *) set);
+			set->memAllocated = set->keeper->endptr - ((char *) set);
 
 			return (MemoryContext) set;
 		}
@@ -555,7 +557,7 @@ AllocSetContextCreateInternal(MemoryContext parent,
 						parent,
 						name);
 
-	((MemoryContext) set)->mem_allocated = firstBlockSize;
+	set->memAllocated = firstBlockSize;
 
 	return (MemoryContext) set;
 }
@@ -617,7 +619,7 @@ AllocSetReset(MemoryContext context)
 		else
 		{
 			/* Normal case, release the block */
-			context->mem_allocated -= block->endptr - ((char*) block);
+			set->memAllocated -= block->endptr - ((char*) block);
 
 #ifdef CLOBBER_FREED_MEMORY
 			wipe_mem(block, block->freeptr - ((char *) block));
@@ -627,7 +629,7 @@ AllocSetReset(MemoryContext context)
 		block = next;
 	}
 
-	Assert(context->mem_allocated == keepersize);
+	Assert(set->memAllocated == keepersize);
 
 	/* Reset block size allocation sequence, too */
 	set->nextBlockSize = set->initBlockSize;
@@ -703,7 +705,7 @@ AllocSetDelete(MemoryContext context)
 		AllocBlock	next = block->next;
 
 		if (block != set->keeper)
-			context->mem_allocated -= block->endptr - ((char *) block);
+			set->memAllocated -= block->endptr - ((char *) block);
 
 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->freeptr - ((char *) block));
@@ -715,7 +717,7 @@ AllocSetDelete(MemoryContext context)
 		block = next;
 	}
 
-	Assert(context->mem_allocated == keepersize);
+	Assert(set->memAllocated == keepersize);
 
 	/* Finally, free the context header, including the keeper block */
 	free(set);
@@ -758,7 +760,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 		if (block == NULL)
 			return NULL;
 
-		context->mem_allocated += blksize;
+		set->memAllocated += blksize;
 
 		block->aset = set;
 		block->freeptr = block->endptr = ((char *) block) + blksize;
@@ -955,7 +957,7 @@ AllocSetAlloc(MemoryContext context, Size size)
 		if (block == NULL)
 			return NULL;
 
-		context->mem_allocated += blksize;
+		set->memAllocated += blksize;
 
 		block->aset = set;
 		block->freeptr = ((char *) block) + ALLOC_BLOCKHDRSZ;
@@ -1058,7 +1060,7 @@ AllocSetFree(MemoryContext context, void *pointer)
 		if (block->next)
 			block->next->prev = block->prev;
 
-		context->mem_allocated -= block->endptr - ((char*) block);
+		set->memAllocated -= block->endptr - ((char*) block);
 
 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->freeptr - ((char *) block));
@@ -1161,8 +1163,8 @@ AllocSetRealloc(MemoryContext context, void *pointer, Size size)
 		}
 
 		/* updated separately, not to underflow when (oldblksize > blksize) */
-		context->mem_allocated -= oldblksize;
-		context->mem_allocated += blksize;
+		set->memAllocated -= oldblksize;
+		set->memAllocated += blksize;
 
 		block->freeptr = block->endptr = ((char *) block) + blksize;
 
@@ -1337,6 +1339,24 @@ AllocSetGetChunkSpace(MemoryContext context, void *pointer)
 	return result;
 }
 
+/*
+ * All memory currently allocated for this context (including fragmentation
+ * and freed chunks).
+ *
+ * Allocation sizes double (up to maxBlockSize), so the current block may
+ * represent half of the total space allocated to the context. Subtract away
+ * the free space at the tail of the current block, which may never have been
+ * touched.
+ */
+static Size
+AllocSetMemAllocated(MemoryContext context)
+{
+	AllocSet set = (AllocSet) context;
+	AllocBlock currentBlock = set->blocks;
+	Size tailSpace = currentBlock->endptr - currentBlock->freeptr;
+	return set->memAllocated - tailSpace;
+}
+
 /*
  * AllocSetIsEmpty
  *		Is an allocset empty of any allocated space?
@@ -1538,7 +1558,7 @@ AllocSetCheck(MemoryContext context)
 				 name, block);
 	}
 
-	Assert(total_allocated == context->mem_allocated);
+	Assert(total_allocated == set->memAllocated);
 }
 
 #endif							/* MEMORY_CONTEXT_CHECKING */

src/backend/utils/mmgr/generation.c

@@ -61,6 +61,7 @@ typedef struct GenerationContext
 
 	/* Generational context parameters */
 	Size		blockSize;		/* standard block size */
+	Size		memAllocated;	/* track memory allocated for this context */
 
 	GenerationBlock *block;		/* current (most recently allocated) block */
 	dlist_head	blocks;			/* list of blocks */
@@ -152,6 +153,7 @@ static void *GenerationRealloc(MemoryContext context, void *pointer, Size size);
 static void GenerationReset(MemoryContext context);
 static void GenerationDelete(MemoryContext context);
 static Size GenerationGetChunkSpace(MemoryContext context, void *pointer);
+static Size GenerationMemAllocated(MemoryContext context);
 static bool GenerationIsEmpty(MemoryContext context);
 static void GenerationStats(MemoryContext context,
 							MemoryStatsPrintFunc printfunc, void *passthru,
@@ -171,6 +173,7 @@ static const MemoryContextMethods GenerationMethods = {
 	GenerationReset,
 	GenerationDelete,
 	GenerationGetChunkSpace,
+	GenerationMemAllocated,
 	GenerationIsEmpty,
 	GenerationStats
 #ifdef MEMORY_CONTEXT_CHECKING
@@ -258,6 +261,7 @@ GenerationContextCreate(MemoryContext parent,
 
 	/* Fill in GenerationContext-specific header fields */
 	set->blockSize = blockSize;
+	set->memAllocated = 0;
 	set->block = NULL;
 	dlist_init(&set->blocks);
 
@@ -297,7 +301,7 @@ GenerationReset(MemoryContext context)
 
 		dlist_delete(miter.cur);
 
-		context->mem_allocated -= block->blksize;
+		set->memAllocated -= block->blksize;
 
 #ifdef CLOBBER_FREED_MEMORY
 		wipe_mem(block, block->blksize);
@@ -354,7 +358,7 @@ GenerationAlloc(MemoryContext context, Size size)
 		if (block == NULL)
 			return NULL;
 
-		context->mem_allocated += blksize;
+		set->memAllocated += blksize;
 
 		/* block with a single (used) chunk */
 		block->blksize = blksize;
@@ -411,7 +415,7 @@ GenerationAlloc(MemoryContext context, Size size)
 		if (block == NULL)
 			return NULL;
 
-		context->mem_allocated += blksize;
+		set->memAllocated += blksize;
 
 		block->blksize = blksize;
 		block->nchunks = 0;
@@ -528,7 +532,7 @@ GenerationFree(MemoryContext context, void *pointer)
 	if (set->block == block)
 		set->block = NULL;
 
-	context->mem_allocated -= block->blksize;
+	set->memAllocated -= block->blksize;
 	free(block);
 }
 
@@ -666,6 +670,17 @@ GenerationGetChunkSpace(MemoryContext context, void *pointer)
 	return result;
 }
 
+/*
+ * All memory currently allocated for this context (including fragmentation
+ * and freed chunks).
+ */
+static Size
+GenerationMemAllocated(MemoryContext context)
+{
+	GenerationContext *set = (GenerationContext *) context;
+	return set->memAllocated;
+}
+
 /*
  * GenerationIsEmpty
  *		Is a GenerationContext empty of any allocated space?
@@ -844,7 +859,7 @@ GenerationCheck(MemoryContext context)
 				 name, nfree, block, block->nfree);
 	}
 
-	Assert(total_allocated == context->mem_allocated);
+	Assert(total_allocated == gen->memAllocated);
 }
 
 #endif							/* MEMORY_CONTEXT_CHECKING */

src/backend/utils/mmgr/mcxt.c

@@ -469,7 +469,7 @@ MemoryContextIsEmpty(MemoryContext context)
 Size
 MemoryContextMemAllocated(MemoryContext context, bool recurse)
 {
-	Size	total = context->mem_allocated;
+	Size	total = context->methods->mem_allocated(context);
 
 	AssertArg(MemoryContextIsValid(context));
 
@@ -760,7 +760,6 @@ MemoryContextCreate(MemoryContext node,
 	node->methods = methods;
 	node->parent = parent;
 	node->firstchild = NULL;
-	node->mem_allocated = 0;
 	node->prevchild = NULL;
 	node->name = name;
 	node->ident = NULL;

src/backend/utils/mmgr/slab.c

@@ -67,6 +67,7 @@ typedef struct SlabContext
 	Size		fullChunkSize;	/* chunk size including header and alignment */
 	Size		blockSize;		/* block size */
 	Size		headerSize;		/* allocated size of context header */
+	Size		memAllocated;	/* track memory allocated for this context */
 	int			chunksPerBlock; /* number of chunks per block */
 	int			minFreeChunks;	/* min number of free chunks in any block */
 	int			nblocks;		/* number of blocks allocated */
@@ -132,6 +133,7 @@ static void *SlabRealloc(MemoryContext context, void *pointer, Size size);
 static void SlabReset(MemoryContext context);
 static void SlabDelete(MemoryContext context);
 static Size SlabGetChunkSpace(MemoryContext context, void *pointer);
+static Size SlabMemAllocated(MemoryContext context);
 static bool SlabIsEmpty(MemoryContext context);
 static void SlabStats(MemoryContext context,
 					  MemoryStatsPrintFunc printfunc, void *passthru,
@@ -150,6 +152,7 @@ static const MemoryContextMethods SlabMethods = {
 	SlabReset,
 	SlabDelete,
 	SlabGetChunkSpace,
+	SlabMemAllocated,
 	SlabIsEmpty,
 	SlabStats
 #ifdef MEMORY_CONTEXT_CHECKING
@@ -262,6 +265,7 @@ SlabContextCreate(MemoryContext parent,
 	slab->fullChunkSize = fullChunkSize;
 	slab->blockSize = blockSize;
 	slab->headerSize = headerSize;
+	slab->memAllocated = 0;
 	slab->chunksPerBlock = chunksPerBlock;
 	slab->minFreeChunks = 0;
 	slab->nblocks = 0;
@@ -286,6 +290,17 @@ SlabContextCreate(MemoryContext parent,
 	return (MemoryContext) slab;
 }
 
+/*
+ * All memory currently allocated for this context (including fragmentation
+ * and freed chunks).
+ */
+static Size
+SlabMemAllocated(MemoryContext context)
+{
+	SlabContext *slab = (SlabContext *) context;
+	return slab->memAllocated;
+}
+
 /*
  * SlabReset
  *		Frees all memory which is allocated in the given set.
@@ -322,14 +337,14 @@ SlabReset(MemoryContext context)
 #endif
 			free(block);
 			slab->nblocks--;
-			context->mem_allocated -= slab->blockSize;
+			slab->memAllocated -= slab->blockSize;
 		}
 	}
 
 	slab->minFreeChunks = 0;
 
 	Assert(slab->nblocks == 0);
-	Assert(context->mem_allocated == 0);
+	Assert(slab->memAllocated == 0);
 }
 
 /*
@@ -407,7 +422,7 @@ SlabAlloc(MemoryContext context, Size size)
 
 		slab->minFreeChunks = slab->chunksPerBlock;
 		slab->nblocks += 1;
-		context->mem_allocated += slab->blockSize;
+		slab->memAllocated += slab->blockSize;
 	}
 
 	/* grab the block from the freelist (even the new block is there) */
@@ -501,7 +516,7 @@ SlabAlloc(MemoryContext context, Size size)
 
 	SlabAllocInfo(slab, chunk);
 
-	Assert(slab->nblocks * slab->blockSize == context->mem_allocated);
+	Assert(slab->nblocks * slab->blockSize == slab->memAllocated);
 
 	return SlabChunkGetPointer(chunk);
 }
@@ -578,13 +593,13 @@ SlabFree(MemoryContext context, void *pointer)
 	{
 		free(block);
 		slab->nblocks--;
-		context->mem_allocated -= slab->blockSize;
+		slab->memAllocated -= slab->blockSize;
 	}
 	else
 		dlist_push_head(&slab->freelist[block->nfree], &block->node);
 
 	Assert(slab->nblocks >= 0);
-	Assert(slab->nblocks * slab->blockSize == context->mem_allocated);
+	Assert(slab->nblocks * slab->blockSize == slab->memAllocated);
 }
 
 /*
@@ -804,7 +819,7 @@ SlabCheck(MemoryContext context)
 		}
 	}
 
-	Assert(slab->nblocks * slab->blockSize == context->mem_allocated);
+	Assert(slab->nblocks * slab->blockSize == slab->memAllocated);
 }
 
 #endif							/* MEMORY_CONTEXT_CHECKING */

src/include/nodes/memnodes.h

@@ -63,6 +63,7 @@ typedef struct MemoryContextMethods
 	void		(*reset) (MemoryContext context);
 	void		(*delete_context) (MemoryContext context);
 	Size		(*get_chunk_space) (MemoryContext context, void *pointer);
+	Size		(*mem_allocated) (MemoryContext context);
 	bool		(*is_empty) (MemoryContext context);
 	void		(*stats) (MemoryContext context,
 						  MemoryStatsPrintFunc printfunc, void *passthru,
@@ -79,7 +80,6 @@ typedef struct MemoryContextData
 	/* these two fields are placed here to minimize alignment wastage: */
 	bool		isReset;		/* T = no space alloced since last reset */
 	bool		allowInCritSection; /* allow palloc in critical section */
-	Size		mem_allocated;	/* track memory allocated for this context */
 	const MemoryContextMethods *methods;	/* virtual function table */
 	MemoryContext parent;		/* NULL if no parent (toplevel context) */
 	MemoryContext firstchild;	/* head of linked list of children */