validation, log: extract FlushSnapshotToDisk() function

This moves the flushing and logging into one method and adds logging
of time duration and memory for the snapshot chainstate flushing.

src/validation.cpp

@@ -4840,6 +4840,20 @@ bool ChainstateManager::ActivateSnapshot(
     return true;
 }
 
+static void FlushSnapshotToDisk(CCoinsViewCache& coins_cache, bool snapshot_loaded)
+{
+    LogPrintf("[snapshot] flushing %s (%.2f MB)... ", /* Continued */
+              snapshot_loaded ? "snapshot chainstate to disk" : "coins cache",
+              coins_cache.DynamicMemoryUsage() / (1000 * 1000));
+
+    const int64_t flush_now{GetTimeMillis()};
+
+    // TODO: if #17487 is merged, add erase=false here if snapshot is loaded, for better performance.
+    coins_cache.Flush();
+
+    LogPrintf("done (%.2fms)\n", GetTimeMillis() - flush_now);
+}
+
 bool ChainstateManager::PopulateAndValidateSnapshot(
     CChainState& snapshot_chainstate,
     CAutoFile& coins_file,
@@ -4877,7 +4891,6 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
     uint64_t coins_left = metadata.m_coins_count;
 
     LogPrintf("[snapshot] loading coins from snapshot %s\n", base_blockhash.ToString());
-    int64_t flush_now{0};
     int64_t coins_processed{0};
 
     while (coins_left > 0) {
@@ -4921,19 +4934,14 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
             const auto snapshot_cache_state = WITH_LOCK(::cs_main,
                 return snapshot_chainstate.GetCoinsCacheSizeState());
 
-            if (snapshot_cache_state >=
-                    CoinsCacheSizeState::CRITICAL) {
-                LogPrintf("[snapshot] flushing coins cache (%.2f MB)... ", /* Continued */
-                    coins_cache.DynamicMemoryUsage() / (1000 * 1000));
-                flush_now = GetTimeMillis();
-
+            if (snapshot_cache_state >= CoinsCacheSizeState::CRITICAL) {
                 // This is a hack - we don't know what the actual best block is, but that
                 // doesn't matter for the purposes of flushing the cache here. We'll set this
                 // to its correct value (`base_blockhash`) below after the coins are loaded.
                 coins_cache.SetBestBlock(GetRandHash());
 
-                coins_cache.Flush();
-                LogPrintf("done (%.2fms)\n", GetTimeMillis() - flush_now);
+                // No need to acquire cs_main since this chainstate isn't being used yet.
+                FlushSnapshotToDisk(coins_cache, /*snapshot_loaded=*/false);
             }
         }
     }
@@ -4963,9 +4971,8 @@ bool ChainstateManager::PopulateAndValidateSnapshot(
         coins_cache.DynamicMemoryUsage() / (1000 * 1000),
         base_blockhash.ToString());
 
-    LogPrintf("[snapshot] flushing snapshot chainstate to disk\n");
     // No need to acquire cs_main since this chainstate isn't being used yet.
-    coins_cache.Flush(); // TODO: if #17487 is merged, add erase=false here for better performance.
+    FlushSnapshotToDisk(coins_cache, /*snapshot_loaded=*/true);
 
     assert(coins_cache.GetBestBlock() == base_blockhash);