From ba626aac5078850cfa494493a271c19c13345ccf Mon Sep 17 00:00:00 2001
From: Martin Vogel <martin.vogel@datadice.io>
Date: Thu, 12 Mar 2026 15:29:22 +0100
Subject: [PATCH] Use dynamic GOMEMLIMIT: 25% of system RAM, clamped to [2GB,
 8GB]

Replace static 2GB default with platform-aware auto-detection:
- Linux: syscall.Sysinfo
- macOS: sysctl hw.memsize
- Windows: GlobalMemoryStatusEx

Falls back to 4GB if detection fails. User config still overrides.
Prevents both OOM kills (upper clamp) and excessive GC pressure (lower clamp).
---
 cmd/codebase-memory-mcp/main.go             | 17 +++++-----
 cmd/codebase-memory-mcp/memlimit.go         | 30 ++++++++++++++++++
 cmd/codebase-memory-mcp/memlimit_darwin.go  | 14 +++++++++
 cmd/codebase-memory-mcp/memlimit_linux.go   | 14 +++++++++
 cmd/codebase-memory-mcp/memlimit_windows.go | 35 +++++++++++++++++++++
 5 files changed, 103 insertions(+), 7 deletions(-)
 create mode 100644 cmd/codebase-memory-mcp/memlimit.go
 create mode 100644 cmd/codebase-memory-mcp/memlimit_darwin.go
 create mode 100644 cmd/codebase-memory-mcp/memlimit_linux.go
 create mode 100644 cmd/codebase-memory-mcp/memlimit_windows.go

diff --git a/cmd/codebase-memory-mcp/main.go b/cmd/codebase-memory-mcp/main.go
index 2aa4d2434..894b67483 100644
--- a/cmd/codebase-memory-mcp/main.go
+++ b/cmd/codebase-memory-mcp/main.go
@@ -67,14 +67,17 @@ func main() {
 		log.Fatalf("config err=%v", err)
 	}
 
-	// Apply GOMEMLIMIT from config (e.g. "2G", "512M"), default 2GB.
-	// Prevents OOM kills on systems without user-configured limits.
-	memLimitStr := cfg.Get(store.ConfigMemLimit, "2G")
-	if limit, parseErr := parseByteSize(memLimitStr); parseErr != nil {
-		log.Printf("config: invalid mem_limit %q: %v", memLimitStr, parseErr)
-		debug.SetMemoryLimit(2 << 30) // fallback: 2GB
+	// Apply GOMEMLIMIT from config (e.g. "4G", "512M").
+	// If not configured, auto-detect: 25% of system memory, clamped to [2GB, 8GB].
+	// Prevents OOM kills while avoiding unnecessary GC pressure.
+	if memLimitStr := cfg.Get(store.ConfigMemLimit, ""); memLimitStr != "" {
+		if limit, parseErr := parseByteSize(memLimitStr); parseErr != nil {
+			log.Printf("config: invalid mem_limit %q: %v", memLimitStr, parseErr)
+		} else {
+			debug.SetMemoryLimit(limit)
+		}
 	} else {
-		debug.SetMemoryLimit(limit)
+		debug.SetMemoryLimit(autoMemLimit())
 	}
 
 	srv := tools.NewServer(router, tools.WithConfig(cfg))
diff --git a/cmd/codebase-memory-mcp/memlimit.go b/cmd/codebase-memory-mcp/memlimit.go
new file mode 100644
index 000000000..279fa9181
--- /dev/null
+++ b/cmd/codebase-memory-mcp/memlimit.go
@@ -0,0 +1,30 @@
+package main
+
+import "log"
+
+const (
+	minMemLimit int64 = 2 << 30 // 2 GB
+	maxMemLimit int64 = 8 << 30 // 8 GB
+	memFraction int64 = 4       // use 1/4 of system memory
+)
+
+// autoMemLimit returns a GOMEMLIMIT value based on available system memory.
+// Uses 25% of total physical RAM, clamped to [2GB, 8GB].
+// Falls back to 4GB if detection fails.
+func autoMemLimit() int64 {
+	total := totalSystemMemory()
+	if total <= 0 {
+		log.Printf("mem_limit: auto-detect unavailable, default=4GB")
+		return 4 << 30
+	}
+
+	limit := total / memFraction
+	if limit < minMemLimit {
+		limit = minMemLimit
+	}
+	if limit > maxMemLimit {
+		limit = maxMemLimit
+	}
+	log.Printf("mem_limit: system=%dGB limit=%dGB", total>>30, limit>>30)
+	return limit
+}
diff --git a/cmd/codebase-memory-mcp/memlimit_darwin.go b/cmd/codebase-memory-mcp/memlimit_darwin.go
new file mode 100644
index 000000000..eb9f722ab
--- /dev/null
+++ b/cmd/codebase-memory-mcp/memlimit_darwin.go
@@ -0,0 +1,14 @@
+//go:build darwin
+
+package main
+
+import "golang.org/x/sys/unix"
+
+// totalSystemMemory returns total physical memory in bytes via sysctl hw.memsize.
+func totalSystemMemory() int64 {
+	mem, err := unix.SysctlUint64("hw.memsize")
+	if err != nil {
+		return 0
+	}
+	return int64(mem)
+}
diff --git a/cmd/codebase-memory-mcp/memlimit_linux.go b/cmd/codebase-memory-mcp/memlimit_linux.go
new file mode 100644
index 000000000..42041de9b
--- /dev/null
+++ b/cmd/codebase-memory-mcp/memlimit_linux.go
@@ -0,0 +1,14 @@
+//go:build linux
+
+package main
+
+import "syscall"
+
+// totalSystemMemory returns total physical memory in bytes via Sysinfo.
+func totalSystemMemory() int64 {
+	var si syscall.Sysinfo_t
+	if err := syscall.Sysinfo(&si); err != nil {
+		return 0
+	}
+	return int64(si.Totalram) * int64(si.Unit)
+}
diff --git a/cmd/codebase-memory-mcp/memlimit_windows.go b/cmd/codebase-memory-mcp/memlimit_windows.go
new file mode 100644
index 000000000..92b8b3718
--- /dev/null
+++ b/cmd/codebase-memory-mcp/memlimit_windows.go
@@ -0,0 +1,35 @@
+//go:build windows
+
+package main
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+// memoryStatusEx mirrors the Windows MEMORYSTATUSEX struct.
+type memoryStatusEx struct {
+	length               uint32
+	memoryLoad           uint32
+	totalPhys            uint64
+	availPhys            uint64
+	totalPageFile        uint64
+	availPageFile        uint64
+	totalVirtual         uint64
+	availVirtual         uint64
+	availExtendedVirtual uint64
+}
+
+// totalSystemMemory returns total physical memory via GlobalMemoryStatusEx.
+func totalSystemMemory() int64 {
+	kernel32 := syscall.NewLazyDLL("kernel32.dll")
+	proc := kernel32.NewProc("GlobalMemoryStatusEx")
+
+	var ms memoryStatusEx
+	ms.length = uint32(unsafe.Sizeof(ms)) //nolint:gosec // standard Windows API pattern
+	r, _, _ := proc.Call(uintptr(unsafe.Pointer(&ms)))
+	if r == 0 {
+		return 0
+	}
+	return int64(ms.totalPhys)
+}