Make lowmem threshold configurable

Author: luke-jr

src/common/system.cpp

@@ -115,16 +115,21 @@ int64_t GetStartupTime()
     return nStartupTime;
 }
 
+size_t g_low_memory_threshold = 10 * 1024 * 1024 /* 10 MB */;
+
 bool SystemNeedsMemoryReleased()
 {
-    constexpr size_t low_memory_threshold = 10 * 1024 * 1024 /* 10 MB */;
+    if (g_low_memory_threshold <= 0) {
+        // Intentionally bypass other metrics when disabled entirely
+        return false;
+    }
 #ifdef WIN32
     MEMORYSTATUSEX mem_status;
     mem_status.dwLength = sizeof(mem_status);
     if (GlobalMemoryStatusEx(&mem_status)) {
         if (mem_status.dwMemoryLoad >= 99 ||
-            mem_status.ullAvailPhys < low_memory_threshold ||
-            mem_status.ullAvailVirtual < low_memory_threshold) {
+            mem_status.ullAvailPhys < g_low_memory_threshold ||
+            mem_status.ullAvailVirtual < g_low_memory_threshold) {
             LogPrintf("%s: YES: %s%% memory load; %s available physical memory; %s available virtual memory\n", __func__, int(mem_status.dwMemoryLoad), size_t(mem_status.ullAvailPhys), size_t(mem_status.ullAvailVirtual));
             return true;
         }
@@ -136,7 +141,7 @@ bool SystemNeedsMemoryReleased()
         // Explicitly 64-bit in case of 32-bit userspace on 64-bit kernel
         const uint64_t free_ram = uint64_t(sys_info.freeram) * sys_info.mem_unit;
         const uint64_t buffer_ram = uint64_t(sys_info.bufferram) * sys_info.mem_unit;
-        if (free_ram + buffer_ram < low_memory_threshold) {
+        if (free_ram + buffer_ram < g_low_memory_threshold) {
             LogPrintf("%s: YES: %s free RAM + %s buffer RAM\n", __func__, free_ram, buffer_ram);
             return true;
         }

src/common/system.h

@@ -25,6 +25,8 @@ std::string ShellEscape(const std::string& arg);
 void runCommand(const std::string& strCommand);
 #endif
 
+extern size_t g_low_memory_threshold;
+
 bool SystemNeedsMemoryReleased();
 
 /**

src/init.cpp

@@ -482,6 +482,7 @@ void SetupServerArgs(ArgsManager& argsman)
     argsman.AddArg("-includeconf=<file>", "Specify additional configuration file, relative to the -datadir path (only useable from configuration file, not command line)", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-allowignoredconf", strprintf("For backwards compatibility, treat an unused %s file in the datadir as a warning, not an error.", BITCOIN_CONF_FILENAME), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-loadblock=<file>", "Imports blocks from external file on startup", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+    argsman.AddArg("-lowmem=<n>", strprintf("If system available memory falls below <n> MiB, flush caches (0 to disable, default: %s)", g_low_memory_threshold / 1024 / 1024), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-maxmempool=<n>", strprintf("Keep the transaction memory pool below <n> megabytes (default: %u)", DEFAULT_MAX_MEMPOOL_SIZE_MB), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-maxorphantx=<n>", strprintf("Keep at most <n> unconnectable transactions in memory (default: %u)", DEFAULT_MAX_ORPHAN_TRANSACTIONS), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-mempoolexpiry=<n>", strprintf("Do not keep transactions in the mempool longer than <n> hours (default: %u)", DEFAULT_MEMPOOL_EXPIRY_HOURS), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
@@ -1491,6 +1492,13 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     }
     LogPrintf("* Using %.1f MiB for in-memory UTXO set (plus up to %.1f MiB of unused mempool space)\n", cache_sizes.coins * (1.0 / 1024 / 1024), mempool_opts.max_size_bytes * (1.0 / 1024 / 1024));
 
+    if (gArgs.IsArgSet("-lowmem")) {
+        g_low_memory_threshold = gArgs.GetIntArg("-lowmem", 0 /* not used */) * 1024 * 1024;
+    }
+    if (g_low_memory_threshold > 0) {
+        LogPrintf("* Flushing caches if available system memory drops below %s MiB\n", g_low_memory_threshold / 1024 / 1024);
+    }
+
     for (bool fLoaded = false; !fLoaded && !ShutdownRequested(node);) {
         node.mempool = std::make_unique<CTxMemPool>(mempool_opts);