[PATCH 3/5] maple_tree: use vacant nodes to reduce worst case allocations
Sidhartha Kumar
sidhartha.kumar at oracle.com
Thu Nov 14 09:05:22 PST 2024
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 allocations.
Rebalancing 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 <sidhartha.kumar at oracle.com>
---
include/linux/maple_tree.h | 2 +
lib/maple_tree.c | 13 +++--
tools/testing/radix-tree/maple.c | 97 +++++++++++++++++++++++++++++---
3 files changed, 100 insertions(+), 12 deletions(-)
diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
index cbbcd18d4186..7d777aa2d9ed 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 21289e350382..f14d70c171c2 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3545,6 +3545,9 @@ 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);
}
@@ -4159,7 +4162,9 @@ static inline void mas_wr_prealloc_setup(struct ma_wr_state *wr_mas)
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:
@@ -4177,13 +4182,13 @@ 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;
+ ret = delta * 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 bc30050227fd..bc8b107e0177 100644
--- a/tools/testing/radix-tree/maple.c
+++ b/tools/testing/radix-tree/maple.c
@@ -35475,12 +35475,85 @@ static void check_dfs_preorder(struct maple_tree *mt)
}
/* End of depth first search tests */
+/* same implementation as mas_is_span_wr() in lib/maple_tree.c */
+static bool is_span_wr(struct ma_state *mas, unsigned long r_max,
+ enum maple_type type, void *entry)
+{
+ unsigned long max = r_max;
+ unsigned long last = mas->last;
+
+ /* Contained in this pivot, fast path */
+ if (last < max)
+ return false;
+
+ if (ma_is_leaf(type)) {
+ max = mas->max;
+ if (last < max)
+ return false;
+ }
+
+ if (last == max) {
+ /*
+ * The last entry of leaf node cannot be NULL unless it is the
+ * rightmost node (writing ULONG_MAX), otherwise it spans slots.
+ */
+ if (entry || last == ULONG_MAX)
+ return false;
+ }
+
+ return true;
+}
+
+/* get height of the lowest non-leaf node with free space */
+static unsigned char get_vacant_height(struct ma_state *mas, void *entry)
+{
+ char vacant_height = 0;
+ enum maple_type type;
+ unsigned long *pivots;
+ unsigned long min = 0;
+ unsigned long max = ULONG_MAX;
+
+ /* start traversal */
+ mas_reset(mas);
+ mas_start(mas);
+ if (!xa_is_node(mas_root(mas)))
+ return 0;
+
+ type = mte_node_type(mas->node);
+ while (!ma_is_leaf(type)) {
+ mas_node_walk(mas, mte_to_node(mas->node), type, &min, &max);
+ mas->end = mas_data_end(mas);
+ pivots = ma_pivots(mte_to_node(mas->node), type);
+
+ if (pivots) {
+ if (mas->offset)
+ min = pivots[mas->offset - 1];
+ if (mas->offset < mas->end)
+ max = pivots[mas->offset];
+ }
+
+ /* detect spanning write */
+ if (is_span_wr(mas, max, type, entry))
+ 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);
@@ -35494,8 +35567,9 @@ 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(&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 +35577,9 @@ 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(&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 +35589,8 @@ 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(&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 +35603,8 @@ 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(&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 +35617,8 @@ 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(&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 +35631,8 @@ 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(&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 +35657,8 @@ 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(&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 +35675,9 @@ 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(&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_store_prealloc(&mas, ptr);
MT_BUG_ON(mt, mas_allocated(&mas) != 0);
mas_set_range(&mas, 0, 200);
--
2.43.0
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