crimson/os/seastore/linked_tree_node: correct balance pivots calculation

for both fixed-kv tree and omap tree

Signed-off-by: Xuehan Xu <[email protected]>

Author: xxhdx1985126

src/crimson/common/fixed_kv_node_layout.h

@@ -558,6 +558,19 @@ class FixedKVNodeLayout {
     set_meta(Meta::merge_from(left.get_meta(), right.get_meta()));
   }
 
+  static uint32_t get_balance_pivot_idx(
+    const FixedKVNodeLayout &left,
+    const FixedKVNodeLayout &right,
+    bool prefer_left)
+  {
+    auto total = left.get_size() + right.get_size();
+    auto pivot_idx = total / 2;
+    if (total % 2 && prefer_left) {
+      pivot_idx++;
+    }
+    return pivot_idx;
+  }
+
   /**
    * balance_into_new_nodes
    *
@@ -574,10 +587,7 @@ class FixedKVNodeLayout {
     FixedKVNodeLayout &replacement_right)
   {
     auto total = left.get_size() + right.get_size();
-    auto pivot_idx = (left.get_size() + right.get_size()) / 2;
-    if (total % 2 && prefer_left) {
-      pivot_idx++;
-    }
+    auto pivot_idx = get_balance_pivot_idx(left, right, prefer_left);
     auto replacement_pivot = pivot_idx >= left.get_size() ?
       right.iter_idx(pivot_idx - left.get_size())->get_key() :
       left.iter_idx(pivot_idx)->get_key();

src/crimson/os/seastore/linked_tree_node.h

@@ -638,11 +638,7 @@ class ParentNode {
   {
     size_t l_size = left.get_size();
     size_t r_size = right.get_size();
-    size_t total = l_size + r_size;
-    size_t pivot_idx = (l_size + r_size) / 2;
-    if (total % 2 && prefer_left) {
-      pivot_idx++;
-    }
+    size_t pivot_idx = T::get_balance_pivot_idx(left, right, prefer_left);
 
     replacement_left.maybe_expand_children(pivot_idx);
     replacement_right.maybe_expand_children(r_size + l_size - pivot_idx);

src/crimson/os/seastore/omap_manager/btree/omap_btree_node_impl.cc

@@ -490,10 +490,10 @@ OMapInnerNode::merge_entry(
       ).si_then([liter=liter, riter=riter, l=l, r=r, oc, this](auto tuple) {
 	LOG_PREFIX(OMapInnerNode::merge_entry);
         auto [replacement_l, replacement_r, replacement_pivot] = tuple;
-	DEBUGT("to update parent: {} {} {}",
-	  oc.t, *this, *replacement_l, *replacement_r);
 	replacement_l->init_range(l->get_begin(), replacement_pivot);
 	replacement_r->init_range(replacement_pivot, r->get_end());
+	DEBUGT("to update parent: {} {} {}",
+	  oc.t, *this, *replacement_l, *replacement_r);
 	if (get_meta().depth > 2) { // l and r are inner nodes
 	  auto &left = *l->template cast<OMapInnerNode>();
 	  auto &right = *r->template cast<OMapInnerNode>();

src/crimson/os/seastore/omap_manager/btree/string_kv_node_layout.h

@@ -738,21 +738,16 @@ class StringKVInnerNodeLayout {
     set_meta(omap_node_meta_t::merge_from(left.get_meta(), right.get_meta()));
   }
 
-  /**
-   * balance_into_new_nodes
-   *
-   * Takes the contents of left and right and copies them into
-   * replacement_left and replacement_right such that
-   * the size of replacement_left just >= 1/2 of (left + right)
-   */
-  static std::string balance_into_new_nodes(
+  static uint32_t get_balance_pivot_idx(
     const StringKVInnerNodeLayout &left,
     const StringKVInnerNodeLayout &right,
-    StringKVInnerNodeLayout &replacement_left,
-    StringKVInnerNodeLayout &replacement_right)
+    // this is just for the consistency with linked tree nodes
+    bool prefer_left = false)
   {
-    uint32_t left_size = omap_inner_key_t(left.get_node_key_ptr()[left.get_size()-1]).key_off;
-    uint32_t right_size = omap_inner_key_t(right.get_node_key_ptr()[right.get_size()-1]).key_off;
+    uint32_t left_size = omap_inner_key_t(
+      left.get_node_key_ptr()[left.get_size()-1]).key_off;
+    uint32_t right_size = omap_inner_key_t(
+      right.get_node_key_ptr()[right.get_size()-1]).key_off;
     uint32_t total = left_size + right_size;
     uint32_t pivot_size = total / 2;
     uint32_t pivot_idx = 0;
@@ -778,6 +773,27 @@ class StringKVInnerNodeLayout {
         }
       }
     }
+    return pivot_idx;
+  }
+
+  /**
+   * balance_into_new_nodes
+   *
+   * Takes the contents of left and right and copies them into
+   * replacement_left and replacement_right such that
+   * the size of replacement_left just >= 1/2 of (left + right)
+   */
+  static std::string balance_into_new_nodes(
+    const StringKVInnerNodeLayout &left,
+    const StringKVInnerNodeLayout &right,
+    StringKVInnerNodeLayout &replacement_left,
+    StringKVInnerNodeLayout &replacement_right)
+  {
+    uint32_t left_size = omap_inner_key_t(left.get_node_key_ptr()[left.get_size()-1]).key_off;
+    uint32_t right_size = omap_inner_key_t(right.get_node_key_ptr()[right.get_size()-1]).key_off;
+    uint32_t total = left_size + right_size;
+    uint32_t pivot_size = total / 2;
+    uint32_t pivot_idx = get_balance_pivot_idx(left, right);
 
     auto replacement_pivot = pivot_idx >= left.get_size() ?
       right.iter_idx(pivot_idx - left.get_size())->get_key() :