From fac9aac82129edd5d77c3aca3e9e6bbf39cc3220 Mon Sep 17 00:00:00 2001
From: sfan5 <sfan5@live.de>
Date: Mon, 17 Jun 2024 15:59:35 +0200
Subject: [PATCH] Move malloc_trim invocations to background thread (#14744)

---
 src/client/mesh_generator_thread.cpp | 15 +++++++++------
 src/emerge.cpp                       |  2 ++
 src/porting.cpp                      | 13 ++++++++++---
 src/porting.h                        | 11 +++++++++--
 4 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/src/client/mesh_generator_thread.cpp b/src/client/mesh_generator_thread.cpp
index 32a01205d..21656aa6e 100644
--- a/src/client/mesh_generator_thread.cpp
+++ b/src/client/mesh_generator_thread.cpp
@@ -24,18 +24,20 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "mapblock.h"
 #include "map.h"
 #include "util/directiontables.h"
+#include "porting.h"
 
-static class BlockPlaceholder {
-public:
-	MapNode data[MAP_BLOCKSIZE * MAP_BLOCKSIZE * MAP_BLOCKSIZE];
+// Data placeholder used for copying from non-existent blocks
+static struct BlockPlaceholder {
+	MapNode data[MapBlock::nodecount];
 
 	BlockPlaceholder()
 	{
-		for (std::size_t i = 0; i < MAP_BLOCKSIZE * MAP_BLOCKSIZE * MAP_BLOCKSIZE; i++)
+		for (std::size_t i = 0; i < MapBlock::nodecount; i++)
 			data[i] = MapNode(CONTENT_IGNORE);
 	}
 
 } block_placeholder;
+
 /*
 	QueuedMeshUpdate
 */
@@ -225,12 +227,13 @@ void MeshUpdateWorkerThread::doUpdate()
 	while ((q = m_queue_in->pop())) {
 		if (m_generation_interval)
 			sleep_ms(m_generation_interval);
+
+		porting::TriggerMemoryTrim();
+
 		ScopeProfiler sp(g_profiler, "Client: Mesh making (sum)");
 
 		MapBlockMesh *mesh_new = new MapBlockMesh(m_client, q->data, *m_camera_offset);
 
-
-
 		MeshUpdateResult r;
 		r.p = q->p;
 		r.mesh = mesh_new;
diff --git a/src/emerge.cpp b/src/emerge.cpp
index d6d6e630a..b53f298b3 100644
--- a/src/emerge.cpp
+++ b/src/emerge.cpp
@@ -662,6 +662,8 @@ void *EmergeThread::run()
 		EmergeAction action;
 		MapBlock *block = nullptr;
 
+		porting::TriggerMemoryTrim();
+
 		if (!popBlockEmerge(&pos, &bedata)) {
 			m_queue_event.wait();
 			continue;
diff --git a/src/porting.cpp b/src/porting.cpp
index 0763e92e1..a7601b101 100644
--- a/src/porting.cpp
+++ b/src/porting.cpp
@@ -920,22 +920,29 @@ double perf_freq = get_perf_freq();
  *
  * As a workaround we track freed memory coarsely and call malloc_trim() once a
  * certain amount is reached.
+ *
+ * Because trimming can take more than 10ms and would cause jitter if done
+ * uncontrolled we have a separate function, which is called from background threads.
  */
 
 static std::atomic<size_t> memory_freed;
 
-constexpr size_t MEMORY_TRIM_THRESHOLD = 128 * 1024 * 1024;
+constexpr size_t MEMORY_TRIM_THRESHOLD = 256 * 1024 * 1024;
 
 void TrackFreedMemory(size_t amount)
+{
+	memory_freed.fetch_add(amount, std::memory_order_relaxed);
+}
+
+void TriggerMemoryTrim()
 {
 	constexpr auto MO = std::memory_order_relaxed;
-	memory_freed.fetch_add(amount, MO);
 	if (memory_freed.load(MO) >= MEMORY_TRIM_THRESHOLD) {
 		// Synchronize call
 		if (memory_freed.exchange(0, MO) < MEMORY_TRIM_THRESHOLD)
 			return;
 		// Leave some headroom for future allocations
-		malloc_trim(1 * 1024 * 1024);
+		malloc_trim(8 * 1024 * 1024);
 	}
 }
 
diff --git a/src/porting.h b/src/porting.h
index 27fabe7cd..b5e23c1f9 100644
--- a/src/porting.h
+++ b/src/porting.h
@@ -290,15 +290,22 @@ void osSpecificInit();
 // This attaches to the parents process console, or creates a new one if it doesnt exist.
 void attachOrCreateConsole();
 
+#if HAVE_MALLOC_TRIM
 /**
  * Call this after freeing bigger blocks of memory. Used on some platforms to
  * properly give memory back to the OS.
  * @param amount Number of bytes freed
 */
-#if HAVE_MALLOC_TRIM
 void TrackFreedMemory(size_t amount);
+
+/**
+ * Call this regularly from background threads. This performs the actual trimming
+ * and is potentially slow.
+ */
+void TriggerMemoryTrim();
 #else
-inline void TrackFreedMemory(size_t amount) { (void)amount; }
+static inline void TrackFreedMemory(size_t amount) { (void)amount; }
+static inline void TriggerMemoryTrim() { (void)0; }
 #endif
 
 #ifdef _WIN32