From f8a9e229deb434b493887ac3c6c387fe599a24c0 Mon Sep 17 00:00:00 2001
From: Jaya Prakash <jayaprakash@ibm.com>
Date: Wed, 12 Mar 2025 19:01:52 +0000
Subject: [PATCH] os/bluestore: Refactor ExtentMap::reshard() into separate
 decision and action phases

Refactored ExtentMap::reshard() by splitting it into two distinct functions:
- reshard_decision(): Determines the resharding plan by analyzing shard distribution, extent sizes, and spanning blob ranges
- reshard_action(): Applies the resharding plan, handling faulting, key removals, and shard updates

Signed-off-by: Jaya Prakash <jayaprakash@ibm.com>
(cherry picked from commit 44f93a610222338f7e763b08fc6c52ac3e82473e)
---
 src/os/bluestore/BlueStore.cc | 69 ++++++++++++++++++++++++++---------
 src/os/bluestore/BlueStore.h  | 17 +++++++++
 2 files changed, 69 insertions(+), 17 deletions(-)

diff --git a/src/os/bluestore/BlueStore.cc b/src/os/bluestore/BlueStore.cc
index 8533d676119..a2f33c26b9f 100644
--- a/src/os/bluestore/BlueStore.cc
+++ b/src/os/bluestore/BlueStore.cc
@@ -3573,11 +3573,9 @@ bid_t BlueStore::ExtentMap::allocate_spanning_blob_id()
   ceph_abort_msg("no available blob id");
 }
 
-void BlueStore::ExtentMap::reshard(
-  KeyValueDB *db,
-  KeyValueDB::Transaction t,
-  uint32_t segment_size)
-{
+BlueStore::ExtentMap::ReshardPlan
+BlueStore::ExtentMap::reshard_decision(uint32_t segment_size) {
+  ReshardPlan plan;
   auto cct = onode->c->store->cct; // used by dout
 
   dout(10) << __func__ << " 0x[" << std::hex << needs_reshard_begin << ","
@@ -3616,7 +3614,6 @@ void BlueStore::ExtentMap::reshard(
     needs_reshard_end = OBJECT_MAX_SIZE;
   }
 
-  fault_range(db, needs_reshard_begin, (needs_reshard_end - needs_reshard_begin));
   uint64_t data_reshard_end = needs_reshard_end;
   if (needs_reshard_end == OBJECT_MAX_SIZE && !extent_map.empty()) {
     data_reshard_end = extent_map.rbegin()->blob_end();
@@ -3628,17 +3625,6 @@ void BlueStore::ExtentMap::reshard(
   uint32_t spanning_scan_begin = needs_reshard_begin;
   uint32_t spanning_scan_end = needs_reshard_end;
 
-  // remove old keys
-  string key;
-  for (unsigned i = shard_index_begin; i < shard_index_end; ++i) {
-    generate_extent_shard_key_and_apply(
-      onode->key, shards[i].shard_info->offset, &key,
-      [&](const string& final_key) {
-	t->rmkey(PREFIX_OBJ, final_key);
-      }
-      );
-  }
-
   // calculate average extent size
   unsigned bytes = 0;
   unsigned extents = 0;
@@ -3745,6 +3731,47 @@ void BlueStore::ExtentMap::reshard(
   auto& extent_map_shards = onode->onode.extent_map_shards;
   dout(20) << __func__ << "  new " << new_shard_info << dendl;
   dout(20) << __func__ << "  old " << extent_map_shards << dendl;
+
+  plan.shard_index_begin = shard_index_begin;
+  plan.shard_index_end = shard_index_end;
+  plan.spanning_scan_begin = spanning_scan_begin;
+  plan.spanning_scan_end = spanning_scan_end;
+  plan.new_shard_info = std::move(new_shard_info);
+  return plan;
+}
+
+
+void BlueStore::ExtentMap::reshard_action(
+  ReshardPlan& plan,
+  KeyValueDB *db,
+  KeyValueDB::Transaction t) {
+  auto cct = onode->c->store->cct; // For configuration and logging
+
+  std::vector<bluestore_onode_t::shard_info> new_shard_info = plan.new_shard_info;
+  unsigned shard_index_begin = plan.shard_index_begin;
+  unsigned shard_index_end = plan.shard_index_end;
+  uint32_t spanning_scan_begin = plan.spanning_scan_begin;
+  uint32_t spanning_scan_end = plan.spanning_scan_end;
+
+  dout(20) << __func__ << " applying plan with shards [" << shard_index_begin << ","
+           << shard_index_end << ")" << dendl;
+
+  // Fault the range
+  fault_range(db, needs_reshard_begin, (needs_reshard_end - needs_reshard_begin));
+
+  // Remove old shard keys
+  string key;
+  for (unsigned i = shard_index_begin; i < shard_index_end; ++i) {
+    generate_extent_shard_key_and_apply(
+      onode->key, shards[i].shard_info->offset, &key,
+      [&](const string& final_key) {
+	t->rmkey(PREFIX_OBJ, final_key);
+      }
+      );
+  }
+
+  // Update extent_map_shards and shards
+  auto& extent_map_shards = onode->onode.extent_map_shards;
   if (extent_map_shards.empty()) {
     // no old shards to keep
     extent_map_shards.swap(new_shard_info);
@@ -3920,6 +3947,14 @@ void BlueStore::ExtentMap::reshard(
   clear_needs_reshard();
 }
 
+void BlueStore::ExtentMap::reshard(
+  KeyValueDB *db,
+  KeyValueDB::Transaction t,
+  uint32_t segment_size) {
+  auto plan = reshard_decision(segment_size);
+  reshard_action(plan, db, t);
+}
+
 bool BlueStore::ExtentMap::encode_some(
   uint32_t offset,
   uint32_t length,
diff --git a/src/os/bluestore/BlueStore.h b/src/os/bluestore/BlueStore.h
index 693d4499a30..b82e119c406 100644
--- a/src/os/bluestore/BlueStore.h
+++ b/src/os/bluestore/BlueStore.h
@@ -1059,6 +1059,23 @@ public:
       bool just_after_reshard //true to indicate that update should now respect shard boundaries
     );                        //as no further resharding will be done
     decltype(BlueStore::Blob::id) allocate_spanning_blob_id();
+
+    struct ReshardPlan {
+      std::vector<bluestore_onode_t::shard_info> new_shard_info;
+      unsigned shard_index_begin;
+      unsigned shard_index_end;
+      uint32_t spanning_scan_begin;
+      uint32_t spanning_scan_end;
+    };
+
+    ReshardPlan reshard_decision(uint32_t segment_size);
+
+    void reshard_action(
+      ReshardPlan& plan,
+      KeyValueDB *db,
+      KeyValueDB::Transaction t);
+
+
     void reshard(
       KeyValueDB *db,
       KeyValueDB::Transaction t,
-- 
2.39.5