Get rid of radix tree's general purpose memory context

Previously, this was notionally used only for the entry point of the
tree and as a convenient parent for other contexts.

For shared memory, the creator previously allocated the entry point
in this context, but attaching backends didn't have access to that,
so they just used the caller's context. For the sake of consistency,
allocate every instance of an entry point in the caller's context.

For local memory, allocate the control object in the caller's context
as well. This commit also makes the "leaf context" the notional parent
of the child contexts used for nodes, so it's a bit of a misnomer,
but a future commit will make the node contexts independent rather
than children, so leave it this way for now to avoid code churn.

The memory context parameter for RT_CREATE is now unused in the case
of shared memory, so remove it and adjust callers to match.

In passing, remove unused "context" member from struct TidStore,
which seems to have been an oversight.

Reviewed by Masahiko Sawada

Discussion: https://postgr.es/m/CANWCAZZDCo4k5oURg_pPxM6+WZ1oiG=sqgjmQiELuyP0Vtrwig@mail.gmail.com

1 files changed, 14 insertions, 21 deletions

diff --git a/src/include/lib/radixtree.h b/src/include/lib/radixtree.h
index d4167503892..c80817da554 100644
--- a/src/include/lib/radixtree.h
+++ b/src/include/lib/radixtree.h
@@ -275,7 +275,7 @@ typedef dsa_pointer RT_HANDLE;
 #endif
 
 #ifdef RT_SHMEM
-RT_SCOPE	RT_RADIX_TREE *RT_CREATE(MemoryContext ctx, dsa_area *dsa, int tranche_id);
+RT_SCOPE	RT_RADIX_TREE *RT_CREATE(dsa_area *dsa, int tranche_id);
 RT_SCOPE	RT_RADIX_TREE *RT_ATTACH(dsa_area *dsa, dsa_pointer dp);
 RT_SCOPE void RT_DETACH(RT_RADIX_TREE * tree);
 RT_SCOPE	RT_HANDLE RT_GET_HANDLE(RT_RADIX_TREE * tree);
@@ -706,8 +706,6 @@ typedef struct RT_RADIX_TREE_CONTROL
 /* Entry point for allocating and accessing the tree */
 struct RT_RADIX_TREE
 {
-	MemoryContext context;
-
 	/* pointing to either local memory or DSA */
 	RT_RADIX_TREE_CONTROL *ctl;
 
@@ -1809,31 +1807,25 @@ have_slot:
 /***************** SETUP / TEARDOWN *****************/
 
 /*
- * Create the radix tree in the given memory context and return it.
+ * Create the radix tree root in the caller's memory context and return it.
  *
- * All local memory required for a radix tree is allocated in the given
- * memory context and its children. Note that RT_FREE() will delete all
- * allocated space within the given memory context, so the dsa_area should
- * be created in a different context.
+ * The tree's nodes and leaves are allocated in "ctx" and its children for
+ * local memory, or in "dsa" for shared memory.
  */
 RT_SCOPE	RT_RADIX_TREE *
 #ifdef RT_SHMEM
-RT_CREATE(MemoryContext ctx, dsa_area *dsa, int tranche_id)
+RT_CREATE(dsa_area *dsa, int tranche_id)
 #else
 RT_CREATE(MemoryContext ctx)
 #endif
 {
 	RT_RADIX_TREE *tree;
-	MemoryContext old_ctx;
 	RT_CHILD_PTR rootnode;
 #ifdef RT_SHMEM
 	dsa_pointer dp;
 #endif
 
-	old_ctx = MemoryContextSwitchTo(ctx);
-
 	tree = (RT_RADIX_TREE *) palloc0(sizeof(RT_RADIX_TREE));
-	tree->context = ctx;
 
 #ifdef RT_SHMEM
 	tree->dsa = dsa;
@@ -1858,7 +1850,7 @@ RT_CREATE(MemoryContext ctx)
 	}
 
 	/* By default we use the passed context for leaves. */
-	tree->leaf_context = tree->context;
+	tree->leaf_context = ctx;
 
 #ifndef RT_VARLEN_VALUE_SIZE
 
@@ -1880,8 +1872,6 @@ RT_CREATE(MemoryContext ctx)
 	tree->ctl->start_shift = 0;
 	tree->ctl->max_val = RT_SHIFT_GET_MAX_VAL(0);
 
-	MemoryContextSwitchTo(old_ctx);
-
 	return tree;
 }
 
@@ -2054,13 +2044,16 @@ RT_FREE(RT_RADIX_TREE * tree)
 	 */
 	tree->ctl->magic = 0;
 	dsa_free(tree->dsa, tree->ctl->handle);
-#endif
-
+#else
 	/*
-	 * Free all space allocated within the tree's context and delete all child
+	 * Free all space allocated within the leaf context and delete all child
 	 * contexts such as those used for nodes.
 	 */
-	MemoryContextReset(tree->context);
+	MemoryContextReset(tree->leaf_context);
+
+	pfree(tree->ctl);
+#endif
+	pfree(tree);
 }
 
 /***************** ITERATION *****************/
@@ -2674,7 +2667,7 @@ RT_MEMORY_USAGE(RT_RADIX_TREE * tree)
 	Assert(tree->ctl->magic == RT_RADIX_TREE_MAGIC);
 	total = dsa_get_total_size(tree->dsa);
 #else
-	total = MemoryContextMemAllocated(tree->context, true);
+	total = MemoryContextMemAllocated(tree->leaf_context, true);
 #endif
 
 	return total;