From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sat, 16 Oct 2021 01:36:00 -0700
Subject: [PATCH] Do not overload I/O threads with chunk data while flush
 saving

If the chunk count is high, then the memory used by the
chunks adds up and could cause problems. By flushing
every so many chunks, the server will not become
stressed for memory. It will also not increase the total
time to save, as flush saving performs a full flush at
the end anyways.

diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
index 952286cca1ce9e893f4a9e5939c552efe975abb4..9ba13ee1df980b9bd5318cefeb3412a8923b66a3 100644
--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
+++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
@@ -928,6 +928,16 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
     // Paper end
 
     protected void saveAllChunks(boolean flush) {
+        // Paper start - do not overload I/O threads with too much work when saving
+        int[] saved = new int[1];
+        int maxAsyncSaves = 50;
+        Runnable onChunkSave = () -> {
+            if (++saved[0] >= maxAsyncSaves) {
+                saved[0] = 0;
+                com.destroystokyo.paper.io.PaperFileIOThread.Holder.INSTANCE.flush();
+            }
+        };
+        // Paper end - do not overload I/O threads with too much work when saving
         if (flush) {
             List<ChunkHolder> list = (List) this.updatingChunks.getVisibleValuesCopy().stream().filter(ChunkHolder::wasAccessibleSinceLastSave).peek(ChunkHolder::refreshAccessibility).collect(Collectors.toList()); // Paper
             MutableBoolean mutableboolean = new MutableBoolean();
@@ -950,6 +960,7 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
                 }).filter((ichunkaccess) -> {
                     return ichunkaccess instanceof ImposterProtoChunk || ichunkaccess instanceof LevelChunk;
                 }).filter(this::save).forEach((ichunkaccess) -> {
+                    onChunkSave.run(); // Paper - do not overload I/O threads with too much work when saving
                     mutableboolean.setTrue();
                 });
             } while (mutableboolean.isTrue());