From 301c6c2690ef47bce41da27323fcbf340eb39888 Mon Sep 17 00:00:00 2001 From: Sidhartha Kumar Date: Mon, 7 Apr 2025 18:40:59 +0000 Subject: [PATCH] maple_tree: use vacant nodes to reduce worst case allocations In order to determine the store type for a maple tree operation, a walk of the tree is done through mas_wr_walk(). This function descends the tree until a spanning write is detected or we reach a leaf node. While descending, keep track of the height at which we encounter a node with available space. This is done by checking if mas->end is less than the number of slots a given node type can fit. Now that the height of the vacant node is tracked, we can use the difference between the height of the tree and the height of the vacant node to know how many levels we will have to propagate creating new nodes. Update mas_prealloc_calc() to consider the vacant height and reduce the number of worst-case allocations. Rebalancing and spanning stores are not supported and fall back to using the full height of the tree for allocations. Update preallocation testing assertions to take into account vacant height. Signed-off-by: Sidhartha Kumar Reviewed-by: Liam R. Howlett --- include/linux/maple_tree.h | 2 + lib/maple_tree.c | 13 ++++-- tools/testing/radix-tree/maple.c | 79 ++++++++++++++++++++++++++++---- 3 files changed, 82 insertions(+), 12 deletions(-) diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h index cbbcd18d41868..7d777aa2d9ed9 100644 --- a/include/linux/maple_tree.h +++ b/include/linux/maple_tree.h @@ -463,6 +463,7 @@ struct ma_wr_state { void __rcu **slots; /* mas->node->slots pointer */ void *entry; /* The entry to write */ void *content; /* The existing entry that is being overwritten */ + unsigned char vacant_height; /* Depth of lowest node with free space */ }; #define mas_lock(mas) spin_lock(&((mas)->tree->ma_lock)) @@ -498,6 +499,7 @@ struct ma_wr_state { .mas = ma_state, \ .content = NULL, \ .entry = wr_entry, \ + .vacant_height = 0 \ } #define MA_TOPIARY(name, tree) \ diff --git a/lib/maple_tree.c b/lib/maple_tree.c index f15611c74f336..066edcab96d76 100644 --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -3543,6 +3543,9 @@ static bool mas_wr_walk(struct ma_wr_state *wr_mas) if (ma_is_leaf(wr_mas->type)) return true; + if (mas->end < mt_slots[wr_mas->type] - 1) + wr_mas->vacant_height = mas->depth + 1; + mas_wr_walk_traverse(wr_mas); } @@ -4158,7 +4161,9 @@ set_content: static inline int mas_prealloc_calc(struct ma_wr_state *wr_mas, void *entry) { struct ma_state *mas = wr_mas->mas; - int ret = mas_mt_height(mas) * 3 + 1; + unsigned char height = mas_mt_height(mas); + int ret = height * 3 + 1; + unsigned char delta = height - wr_mas->vacant_height; switch (mas->store_type) { case wr_invalid: @@ -4176,13 +4181,13 @@ static inline int mas_prealloc_calc(struct ma_wr_state *wr_mas, void *entry) ret = 0; break; case wr_spanning_store: - ret = mas_mt_height(mas) * 3 + 1; + WARN_ON_ONCE(ret != height * 3 + 1); break; case wr_split_store: - ret = mas_mt_height(mas) * 2 + 1; + ret = delta * 2 + 1; break; case wr_rebalance: - ret = mas_mt_height(mas) * 2 - 1; + ret = height * 2 + 1; break; case wr_node_store: ret = mt_in_rcu(mas->tree) ? 1 : 0; diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c index e0f8fabe88216..e37a3ab2e921c 100644 --- a/tools/testing/radix-tree/maple.c +++ b/tools/testing/radix-tree/maple.c @@ -35475,15 +35475,65 @@ static void check_dfs_preorder(struct maple_tree *mt) } /* End of depth first search tests */ +/* get height of the lowest non-leaf node with free space */ +static unsigned char get_vacant_height(struct ma_wr_state *wr_mas, void *entry) +{ + struct ma_state *mas = wr_mas->mas; + char vacant_height = 0; + enum maple_type type; + unsigned long *pivots; + unsigned long min = 0; + unsigned long max = ULONG_MAX; + unsigned char offset; + + /* start traversal */ + mas_reset(mas); + mas_start(mas); + if (!xa_is_node(mas_root(mas))) + return 0; + + type = mte_node_type(mas->node); + wr_mas->type = type; + while (!ma_is_leaf(type)) { + mas_node_walk(mas, mte_to_node(mas->node), type, &min, &max); + offset = mas->offset; + mas->end = mas_data_end(mas); + pivots = ma_pivots(mte_to_node(mas->node), type); + + if (pivots) { + if (offset) + min = pivots[mas->offset - 1]; + if (offset < mas->end) + max = pivots[mas->offset]; + } + wr_mas->r_max = offset < mas->end ? pivots[offset] : mas->max; + + /* detect spanning write */ + if (mas_is_span_wr(wr_mas)) + break; + + if (mas->end < mt_slot_count(mas->node) - 1) + vacant_height = mas->depth + 1; + + mas_descend(mas); + type = mte_node_type(mas->node); + mas->depth++; + } + + return vacant_height; +} + /* Preallocation testing */ static noinline void __init check_prealloc(struct maple_tree *mt) { unsigned long i, max = 100; unsigned long allocated; unsigned char height; + unsigned char vacant_height; struct maple_node *mn; void *ptr = check_prealloc; MA_STATE(mas, mt, 10, 20); + MA_WR_STATE(wr_mas, &mas, ptr); mt_set_non_kernel(1000); for (i = 0; i <= max; i++) @@ -35494,8 +35544,9 @@ static noinline void __init check_prealloc(struct maple_tree *mt) MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); allocated = mas_allocated(&mas); height = mas_mt_height(&mas); + vacant_height = get_vacant_height(&wr_mas, ptr); MT_BUG_ON(mt, allocated == 0); - MT_BUG_ON(mt, allocated != 1 + height * 3); + MT_BUG_ON(mt, allocated != 1 + (height - vacant_height) * 3); mas_destroy(&mas); allocated = mas_allocated(&mas); MT_BUG_ON(mt, allocated != 0); @@ -35503,8 +35554,9 @@ static noinline void __init check_prealloc(struct maple_tree *mt) MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); allocated = mas_allocated(&mas); height = mas_mt_height(&mas); + vacant_height = get_vacant_height(&wr_mas, ptr); MT_BUG_ON(mt, allocated == 0); - MT_BUG_ON(mt, allocated != 1 + height * 3); + MT_BUG_ON(mt, allocated != 1 + (height - vacant_height) * 3); MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); mas_destroy(&mas); allocated = mas_allocated(&mas); @@ -35514,7 +35566,8 @@ static noinline void __init check_prealloc(struct maple_tree *mt) MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); allocated = mas_allocated(&mas); height = mas_mt_height(&mas); - MT_BUG_ON(mt, allocated != 1 + height * 3); + vacant_height = get_vacant_height(&wr_mas, ptr); + MT_BUG_ON(mt, allocated != 1 + (height - vacant_height) * 3); mn = mas_pop_node(&mas); MT_BUG_ON(mt, mas_allocated(&mas) != allocated - 1); mn->parent = ma_parent_ptr(mn); @@ -35527,7 +35580,8 @@ static noinline void __init check_prealloc(struct maple_tree *mt) MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); allocated = mas_allocated(&mas); height = mas_mt_height(&mas); - MT_BUG_ON(mt, allocated != 1 + height * 3); + vacant_height = get_vacant_height(&wr_mas, ptr); + MT_BUG_ON(mt, allocated != 1 + (height - vacant_height) * 3); mn = mas_pop_node(&mas); MT_BUG_ON(mt, mas_allocated(&mas) != allocated - 1); MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); @@ -35540,7 +35594,8 @@ static noinline void __init check_prealloc(struct maple_tree *mt) MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); allocated = mas_allocated(&mas); height = mas_mt_height(&mas); - MT_BUG_ON(mt, allocated != 1 + height * 3); + vacant_height = get_vacant_height(&wr_mas, ptr); + MT_BUG_ON(mt, allocated != 1 + (height - vacant_height) * 3); mn = mas_pop_node(&mas); MT_BUG_ON(mt, mas_allocated(&mas) != allocated - 1); mas_push_node(&mas, mn); @@ -35553,7 +35608,8 @@ static noinline void __init check_prealloc(struct maple_tree *mt) MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); allocated = mas_allocated(&mas); height = mas_mt_height(&mas); - MT_BUG_ON(mt, allocated != 1 + height * 3); + vacant_height = get_vacant_height(&wr_mas, ptr); + MT_BUG_ON(mt, allocated != 1 + (height - vacant_height) * 3); mas_store_prealloc(&mas, ptr); MT_BUG_ON(mt, mas_allocated(&mas) != 0); @@ -35578,7 +35634,8 @@ static noinline void __init check_prealloc(struct maple_tree *mt) MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); allocated = mas_allocated(&mas); height = mas_mt_height(&mas); - MT_BUG_ON(mt, allocated != 1 + height * 2); + vacant_height = get_vacant_height(&wr_mas, ptr); + MT_BUG_ON(mt, allocated != 1 + (height - vacant_height) * 2); mas_store_prealloc(&mas, ptr); MT_BUG_ON(mt, mas_allocated(&mas) != 0); mt_set_non_kernel(1); @@ -35595,8 +35652,14 @@ static noinline void __init check_prealloc(struct maple_tree *mt) MT_BUG_ON(mt, mas_preallocate(&mas, ptr, GFP_KERNEL) != 0); allocated = mas_allocated(&mas); height = mas_mt_height(&mas); + vacant_height = get_vacant_height(&wr_mas, ptr); MT_BUG_ON(mt, allocated == 0); - MT_BUG_ON(mt, allocated != 1 + height * 3); + /* + * vacant height cannot be used to compute the number of nodes needed + * as the root contains two entries which means it is on the verge of + * insufficiency. The worst case full height of the tree is needed. + */ + MT_BUG_ON(mt, allocated != height * 3 + 1); mas_store_prealloc(&mas, ptr); MT_BUG_ON(mt, mas_allocated(&mas) != 0); mas_set_range(&mas, 0, 200); -- 2.50.1