crimson/os/seastore/omap_manager: add get_balance_pivot_idx to

StringKVLeafNodeLayout

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

Author: xxhdx1985126

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

@@ -1380,21 +1380,14 @@ class StringKVLeafNodeLayout {
     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 side just >= 1/2 of the total size (left + right).
-   */
-  static std::string balance_into_new_nodes(
+  static std::optional<uint32_t> get_balance_pivot_idx(
     const StringKVLeafNodeLayout &left,
-    const StringKVLeafNodeLayout &right,
-    StringKVLeafNodeLayout &replacement_left,
-    StringKVLeafNodeLayout &replacement_right)
+    const StringKVLeafNodeLayout &right)
   {
-    uint32_t left_size = omap_leaf_key_t(left.get_node_key_ptr()[left.get_size()-1]).key_off;
-    uint32_t right_size = omap_leaf_key_t(right.get_node_key_ptr()[right.get_size()-1]).key_off;
+    uint32_t left_size = omap_leaf_key_t(
+      left.get_node_key_ptr()[left.get_size()-1]).key_off;
+    uint32_t right_size = omap_leaf_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;
@@ -1420,6 +1413,29 @@ class StringKVLeafNodeLayout {
         }
       }
     }
+    return pivot_idx == left.get_size()
+      ? std::nullopt
+      : std::make_optional<uint32_t>(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 side just >= 1/2 of the total size (left + right).
+   */
+  static std::string balance_into_new_nodes(
+    const StringKVLeafNodeLayout &left,
+    const StringKVLeafNodeLayout &right,
+    uint32_t pivot_idx,
+    StringKVLeafNodeLayout &replacement_left,
+    StringKVLeafNodeLayout &replacement_right)
+  {
+    uint32_t left_size = omap_leaf_key_t(left.get_node_key_ptr()[left.get_size()-1]).key_off;
+    uint32_t right_size = omap_leaf_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;
 
     auto replacement_pivot = pivot_idx >= left.get_size() ?
       right.iter_idx(pivot_idx - left.get_size())->get_key() :