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Go Back   Linux Archive > Redhat > Device-mapper Development

 
 
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Old 02-02-2012, 03:39 PM
Joe Thornber
 
Default btree-remove - fix rebalancing of 3 nodes.

When we remove an entry from a node we sometimes rebalance with it's
neighbours. This wasn't being done correctly.
---
drivers/md/persistent-data/dm-btree-remove.c | 174 +++++++++++++++-----------
1 files changed, 99 insertions(+), 75 deletions(-)

diff --git a/drivers/md/persistent-data/dm-btree-remove.c b/drivers/md/persistent-data/dm-btree-remove.c
index 8576d56..aa71e23 100644
--- a/drivers/md/persistent-data/dm-btree-remove.c
+++ b/drivers/md/persistent-data/dm-btree-remove.c
@@ -128,18 +128,9 @@ static void delete_at(struct node *n, unsigned index)
n->header.nr_entries = cpu_to_le32(nr_entries - 1);
}

-static unsigned del_threshold(struct node *n)
-{
- return le32_to_cpu(n->header.max_entries) / 3;
-}
-
static unsigned merge_threshold(struct node *n)
{
- /*
- * The extra one is because we know we're potentially going to
- * delete an entry.
- */
- return 2 * (le32_to_cpu(n->header.max_entries) / 3) + 1;
+ return le32_to_cpu(n->header.max_entries) / 3;
}

struct child {
@@ -188,6 +179,15 @@ static int exit_child(struct dm_btree_info *info, struct child *c)

static void shift(struct node *left, struct node *right, int count)
{
+ uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
+ uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
+ uint32_t max_entries = le32_to_cpu(left->header.max_entries);
+ uint32_t r_max_entries = le32_to_cpu(right->header.max_entries);
+
+ BUG_ON(max_entries != r_max_entries);
+ BUG_ON(nr_left - count > max_entries);
+ BUG_ON(nr_right + count > max_entries);
+
if (!count)
return;

@@ -199,13 +199,8 @@ static void shift(struct node *left, struct node *right, int count)
node_shift(right, count);
}

- left->header.nr_entries =
- cpu_to_le32(le32_to_cpu(left->header.nr_entries) - count);
- BUG_ON(le32_to_cpu(left->header.nr_entries) > le32_to_cpu(left->header.max_entries));
-
- right->header.nr_entries =
- cpu_to_le32(le32_to_cpu(right->header.nr_entries) + count);
- BUG_ON(le32_to_cpu(right->header.nr_entries) > le32_to_cpu(right->header.max_entries));
+ left->header.nr_entries = cpu_to_le32(nr_left - count);
+ right->header.nr_entries = cpu_to_le32(nr_right + count);
}

static void __rebalance2(struct dm_btree_info *info, struct node *parent,
@@ -215,8 +210,9 @@ static void __rebalance2(struct dm_btree_info *info, struct node *parent,
struct node *right = r->n;
uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
+ unsigned threshold = 2 * merge_threshold(left) + 1;

- if (nr_left + nr_right <= merge_threshold(left)) {
+ if (nr_left + nr_right < threshold) {
/*
* Merge
*/
@@ -234,9 +230,6 @@ static void __rebalance2(struct dm_btree_info *info, struct node *parent,
* Rebalance.
*/
unsigned target_left = (nr_left + nr_right) / 2;
- unsigned shift_ = nr_left - target_left;
- BUG_ON(le32_to_cpu(left->header.max_entries) <= nr_left - shift_);
- BUG_ON(le32_to_cpu(right->header.max_entries) <= nr_right + shift_);
shift(left, right, nr_left - target_left);
*key_ptr(parent, r->index) = right->keys[0];
}
@@ -272,6 +265,84 @@ static int rebalance2(struct shadow_spine *s, struct dm_btree_info *info,
return exit_child(info, &right);
}

+/*
+ * We dump as many entries from center as possible into left, then the rest
+ * in right, then rebalance2. This wastes some cpu, but I want something
+ * simple atm.
+ */
+static void delete_center_node(struct dm_btree_info *info, struct node *parent,
+ struct child *l, struct child *c, struct child *r,
+ struct node *left, struct node *center, struct node *right,
+ uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
+{
+ uint32_t max_entries = le32_to_cpu(left->header.max_entries);
+ unsigned shift = min(max_entries - nr_left, nr_center);
+
+ BUG_ON(nr_left + shift > max_entries);
+ node_copy(left, center, -shift);
+ left->header.nr_entries = cpu_to_le32(nr_left + shift);
+
+ if (shift != nr_center) {
+ shift = nr_center - shift;
+ BUG_ON((nr_right + shift) > max_entries);
+ node_shift(right, shift);
+ node_copy(center, right, shift);
+ right->header.nr_entries = cpu_to_le32(nr_right + shift);
+ }
+ *key_ptr(parent, r->index) = right->keys[0];
+
+ delete_at(parent, c->index);
+ r->index--;
+
+ dm_tm_dec(info->tm, dm_block_location(c->block));
+ __rebalance2(info, parent, l, r);
+}
+
+/*
+ * Redistributes entries among 3 sibling nodes.
+ */
+static void redistribute3(struct dm_btree_info *info, struct node *parent,
+ struct child *l, struct child *c, struct child *r,
+ struct node *left, struct node *center, struct node *right,
+ uint32_t nr_left, uint32_t nr_center, uint32_t nr_right)
+{
+ int s;
+ uint32_t max_entries = le32_to_cpu(left->header.max_entries);
+ unsigned target = (nr_left + nr_center + nr_right) / 3;
+ BUG_ON(target > max_entries);
+
+ if (nr_left < nr_right) {
+ s = nr_left - target;
+
+ if (s < 0 && nr_center < -s) {
+ /* not enough in central node */
+ shift(left, center, nr_center);
+ s = nr_center - target;
+ shift(left, right, s);
+ nr_right += s;
+ } else
+ shift(left, center, s);
+
+ shift(center, right, target - nr_right);
+
+ } else {
+ s = target - nr_right;
+ if (s > 0 && nr_center < s) {
+ /* not enough in central node */
+ shift(center, right, nr_center);
+ s = target - nr_center;
+ shift(left, right, s);
+ nr_left -= s;
+ } else
+ shift(center, right, s);
+
+ shift(left, center, nr_left - target);
+ }
+
+ *key_ptr(parent, c->index) = center->keys[0];
+ *key_ptr(parent, r->index) = right->keys[0];
+}
+
static void __rebalance3(struct dm_btree_info *info, struct node *parent,
struct child *l, struct child *c, struct child *r)
{
@@ -282,62 +353,18 @@ static void __rebalance3(struct dm_btree_info *info, struct node *parent,
uint32_t nr_left = le32_to_cpu(left->header.nr_entries);
uint32_t nr_center = le32_to_cpu(center->header.nr_entries);
uint32_t nr_right = le32_to_cpu(right->header.nr_entries);
- uint32_t max_entries = le32_to_cpu(left->header.max_entries);

- unsigned target;
+ unsigned threshold = merge_threshold(left) * 4 + 1;

BUG_ON(left->header.max_entries != center->header.max_entries);
BUG_ON(center->header.max_entries != right->header.max_entries);

- if (((nr_left + nr_center + nr_right) / 2) < merge_threshold(center)) {
- /*
- * Delete center node:
- *
- * We dump as many entries from center as possible into
- * left, then the rest in right, then rebalance2. This
- * wastes some cpu, but I want something simple atm.
- */
- unsigned shift = min(max_entries - nr_left, nr_center);
-
- BUG_ON(nr_left + shift > max_entries);
- node_copy(left, center, -shift);
- left->header.nr_entries = cpu_to_le32(nr_left + shift);
-
- if (shift != nr_center) {
- shift = nr_center - shift;
- BUG_ON((nr_right + shift) >= max_entries);
- node_shift(right, shift);
- node_copy(center, right, shift);
- right->header.nr_entries = cpu_to_le32(nr_right + shift);
- }
- *key_ptr(parent, r->index) = right->keys[0];
-
- delete_at(parent, c->index);
- r->index--;
-
- dm_tm_dec(info->tm, dm_block_location(c->block));
- __rebalance2(info, parent, l, r);
-
- return;
- }
-
- /*
- * Rebalance
- */
- target = (nr_left + nr_center + nr_right) / 3;
- BUG_ON(target > max_entries);
-
- /*
- * Adjust the left node
- */
- shift(left, center, nr_left - target);
-
- /*
- * Adjust the right node
- */
- shift(center, right, target - nr_right);
- *key_ptr(parent, c->index) = center->keys[0];
- *key_ptr(parent, r->index) = right->keys[0];
+ if ((nr_left + nr_center + nr_right) < threshold)
+ delete_center_node(info, parent, l, c, r, left, center, right,
+ nr_left, nr_center, nr_right);
+ else
+ redistribute3(info, parent, l, c, r, left, center, right,
+ nr_left, nr_center, nr_right);
}

static int rebalance3(struct shadow_spine *s, struct dm_btree_info *info,
@@ -441,9 +468,6 @@ static int rebalance_children(struct shadow_spine *s,
if (r)
return r;

- if (child_entries > del_threshold(n))
- return 0;
-
has_left_sibling = i > 0;
has_right_sibling = i < (le32_to_cpu(n->header.nr_entries) - 1);

--
1.7.5.4

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