From 4b209db82cf21d26b55a4764dd0a023037b732a5 Mon Sep 17 00:00:00 2001
From: CamilleLaVey <camillelavey99@gmail.com>
Date: Sat, 1 Aug 2026 23:20:41 -0400
Subject: [PATCH] Request maximum map counts

---
 src/common/host_memory.cpp   | 12 ++++++++++--
 src/common/memory_detect.cpp | 17 +++++++++++++++++
 src/common/memory_detect.h   |  2 ++
 3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/src/common/host_memory.cpp b/src/common/host_memory.cpp
index bae706e6ca..cb7ec1ffa7 100644
--- a/src/common/host_memory.cpp
+++ b/src/common/host_memory.cpp
@@ -683,7 +683,15 @@ public:
                      total_physical >> 20, MinimumTotalPhysical >> 20);
             return 0;
         }
+        const u64 max_map_count = Common::GetMaxMapCount();
+        constexpr u64 ReservedMaps = 24576;
+        if (max_map_count == 0 || max_map_count <= ReservedMaps) {
+            LOG_WARNING(HW_Memory,
+                        "Skipping hardware buffer backing, vm.max_map_count is unknown or too low");
+            return 0;
+        }
         u64 budget = total_physical / 6;
+        budget = (std::min)(budget, (max_map_count - ReservedMaps) * PageAlignment);
         const u64 available = Common::GetAvailablePhysicalMemory();
         if (available != 0) {
             constexpr u64 Headroom = 2ULL << 30;
@@ -695,8 +703,8 @@ public:
         if (budget < MinimumBudget) {
             LOG_INFO(HW_Memory,
                      "Skipping hardware buffer backing, only {} MiB could be committed on a {} MiB "
-                     "system with {} MiB available",
-                     budget >> 20, total_physical >> 20, available >> 20);
+                     "system with {} MiB available and vm.max_map_count {}",
+                     budget >> 20, total_physical >> 20, available >> 20, max_map_count);
             return 0;
         }
         return static_cast<size_t>(budget);
diff --git a/src/common/memory_detect.cpp b/src/common/memory_detect.cpp
index d7d8a0741d..d0f9518bf5 100644
--- a/src/common/memory_detect.cpp
+++ b/src/common/memory_detect.cpp
@@ -107,4 +107,21 @@ u64 GetAvailablePhysicalMemory() {
 #endif
 }
 
+u64 GetMaxMapCount() {
+#ifdef __linux__
+    if (std::FILE* const file = std::fopen("/proc/sys/vm/max_map_count", "re")) {
+        char line[32];
+        u64 count = 0;
+        if (std::fgets(line, sizeof(line), file) != nullptr) {
+            count = std::strtoull(line, nullptr, 10);
+        }
+        std::fclose(file);
+        return count;
+    }
+    return 0;
+#else
+    return 0;
+#endif
+}
+
 } // namespace Common
diff --git a/src/common/memory_detect.h b/src/common/memory_detect.h
index 7141df1172..3bf013b79a 100644
--- a/src/common/memory_detect.h
+++ b/src/common/memory_detect.h
@@ -20,4 +20,6 @@ struct MemoryInfo {
 
 [[nodiscard]] u64 GetAvailablePhysicalMemory();
 
+[[nodiscard]] u64 GetMaxMapCount();
+
 } // namespace Common