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

1 files changed, 33 insertions, 13 deletions

diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index c0623f106d2..ccf78ffe0cb 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/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;
 
@@ -1338,6 +1340,24 @@ AllocSetGetChunkSpace(MemoryContext context, void *pointer)
 }
 
 /*
+ * 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 */