Push dedicated BumpBlocks to the tail of the blocks list

david-rowley · david-rowley · commit 6d2fd66b9908 · 2024-04-17T10:40:31.000+12:00
BumpContext relies on using the head block from its 'blocks' field to use as the current block to allocate new chunks to. When we receive an allocation request larger than allocChunkLimit, we place these chunks on a new dedicated block and, until now, we pushed the block onto the *head* of the 'blocks' list. This behavior caused the previous bump block to no longer be available for new normal-sized (non-large) allocations and would result in blocks only being partially filled if a large allocation request arrived before the block became full. Here adjust the code to push these dedicated blocks onto the *tail* of the blocks list so that the head block remains intact and available to be used by normal allocation request sizes until it becomes full. In passing, make the elog(ERROR) calls for the unsupported callbacks consistent. Likewise for the header comments for those functions. Discussion: https://postgr.es/m/CAApHDvp9___r-ayJj0nZ6GD3MeCGwGZ0_6ZptWpwj+zqHtmwCw@mail.gmail.com Discussion: https://postgr.es/m/CAApHDvqerXpzUnuDQfUEi3DZA+9=Ud9WSt3ruxN5b6PcOosx2g@mail.gmail.com
diff --git a/src/backend/utils/mmgr/bump.c b/src/backend/utils/mmgr/bump.c
@@ -342,8 +342,12 @@ BumpAllocLarge(MemoryContext context, Size size, int flags)
 	randomize_mem((char *) MemoryChunkGetPointer(chunk), size);
 #endif
 
-	/* add the block to the list of allocated blocks */
-	dlist_push_head(&set->blocks, &block->node);
+	/*
+	 * Add the block to the tail of allocated blocks list.  The current block
+	 * is left at the head of the list as it may still have space for
+	 * non-large allocations.
+	 */
+	dlist_push_tail(&set->blocks, &block->node);
 
 #ifdef MEMORY_CONTEXT_CHECKING
 	/* Ensure any padding bytes are marked NOACCESS. */
@@ -612,7 +616,7 @@ BumpBlockFree(BumpContext *set, BumpBlock *block)
 void
 BumpFree(void *pointer)
 {
-	elog(ERROR, "pfree is not supported by the bump memory allocator");
+	elog(ERROR, "%s is not supported by the bump memory allocator", "pfree");
 }
 
 /*
@@ -638,10 +642,9 @@ BumpGetChunkContext(void *pointer)
 }
 
 /*
-* BumpGetChunkSpace
-*		Given a currently-allocated chunk, determine the total space
-*		it occupies (including all memory-allocation overhead).
-*/
+ * BumpGetChunkSpace
+ *		Unsupported.
+ */
 Size
 BumpGetChunkSpace(void *pointer)
 {
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
@@ -47,7 +47,7 @@ select name, parent, total_bytes > 0, total_nblocks, free_bytes > 0, free_chunks
 from pg_backend_memory_contexts where name = 'Caller tuples';
      name      |     parent     | ?column? | total_nblocks | ?column? | free_chunks 
 ---------------+----------------+----------+---------------+----------+-------------
- Caller tuples | TupleSort sort | t        |             3 | t        |           0
+ Caller tuples | TupleSort sort | t        |             2 | t        |           0
 (1 row)
 
 rollback;
