On 11/15/24 2:52 AM, Wei Yang wrote:
On Thu, Nov 14, 2024 at 12:05:22PM -0500, Sidhartha Kumar wrote:
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@xxxxxxxxxx>
---
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 */
^^^ ^^^
Would this be a little misleading?
Could you elaborate on how its misleading?
};
#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;
For some cases in rebalance, we may split data into three parts, which means
we need 2 extra vacant slot.
Maybe this check is not accurate?
The triple split scenario which you are describing comes from the
spanning store case not on the wr_rebalance case. There is a check
before we set vacant height to return if is_span_wr() so I believe this
is correct still.
+
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;
Hmm... I am afraid we need to put this patch after next one.
Without the change in next patch, we still need to go up the tree till root to
rebalance.
I think you are right here as mas_wr_spanning_store() calls
mas_spanning_rebalance(), I'll switch the order of patch 3 and patch 4.
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;
Looks current calculation is not correct?
If so, do we need to have a fix to be backported?
This was a typo, it can remain as height * 2 -1.
Thanks for taking a look,
Sidhartha Kumar
