v4-0003-Always-use-the-caller-provided-context-for-radix-.patch

From 679cf5c305b3f0affb5c4a679cf18eb0674e8691 Mon Sep 17 00:00:00 2001
From: John Naylor <john.naylor@postgresql.org>
Date: Fri, 20 Dec 2024 14:48:24 +0700
Subject: [PATCH v4 3/3] Always use the caller-provided context for radix tree
 leaves

Previously, it may not have worked for a caller to pass a slab context,
since it would have been also used for other things which may have
incompatible size. In an attempt to helpfully avoid wasting space due
to aset's power-of-two rounding, RT_CREATE would create an additional
slab context if the values were fixed-length and larger than pointer
size. The problem was, we have since added the bump context type,
and the generation context was a possibility as well, so silently
overriding the caller's choice is not friendly.

Commit XXXXXXXXX arranged so that the caller-provided context is
only used for leaves and nothing else, so it's safe for the caller
to use slab here if they wish. As demonstration, use slab in one of
the radix tree regression tests.

Reviewed by Masahiko Sawada
---
 src/include/lib/radixtree.h                      | 14 --------------
 src/test/modules/test_radixtree/test_radixtree.c |  5 +++--
 2 files changed, 3 insertions(+), 16 deletions(-)

diff --git a/src/include/lib/radixtree.h b/src/include/lib/radixtree.h
index 97aff227c5..fc7474e0c7 100644
--- a/src/include/lib/radixtree.h
+++ b/src/include/lib/radixtree.h
@@ -1849,21 +1849,7 @@ RT_CREATE(MemoryContext ctx)
 												size_class.allocsize);
 	}
 
-	/* By default we use the passed context for leaves. */
 	tree->leaf_context = ctx;
-
-#ifndef RT_VARLEN_VALUE_SIZE
-
-	/*
-	 * For leaves storing fixed-length values, we use a slab context to avoid
-	 * the possibility of space wastage by power-of-2 rounding up.
-	 */
-	if (sizeof(RT_VALUE_TYPE) > sizeof(RT_PTR_ALLOC))
-		tree->leaf_context = SlabContextCreate(ctx,
-											   RT_STR(RT_PREFIX) "_radix_tree leaf context",
-											   RT_SLAB_BLOCK_SIZE(sizeof(RT_VALUE_TYPE)),
-											   sizeof(RT_VALUE_TYPE));
-#endif							/* !RT_VARLEN_VALUE_SIZE */
 #endif							/* RT_SHMEM */
 
 	/* add root node now so that RT_SET can assume it exists */
diff --git a/src/test/modules/test_radixtree/test_radixtree.c b/src/test/modules/test_radixtree/test_radixtree.c
index 8074b83695..5c54962edf 100644
--- a/src/test/modules/test_radixtree/test_radixtree.c
+++ b/src/test/modules/test_radixtree/test_radixtree.c
@@ -313,9 +313,10 @@ test_random(void)
 #else
 	MemoryContext radixtree_ctx;
 
-	radixtree_ctx = AllocSetContextCreate(CurrentMemoryContext,
+	radixtree_ctx = SlabContextCreate(CurrentMemoryContext,
 										  "test_radix_tree",
-										  ALLOCSET_SMALL_SIZES);
+										  SLAB_DEFAULT_BLOCK_SIZE,
+										  sizeof(TestValueType));
 	radixtree = rt_create(radixtree_ctx);
 #endif
 
-- 
2.47.1