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, 22 insertions, 7 deletions

diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index c928476c479..63750fbc81f 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/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;
@@ -287,6 +291,17 @@ SlabContextCreate(MemoryContext parent,
 }
 
 /*
+ * 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 */