From c04540a2db4c90018a2bc420372ea43d3b0e33bf Mon Sep 17 00:00:00 2001
From: jonny rhea <5555162+jrhea@users.noreply.github.com>
Date: Thu, 9 Jul 2026 16:58:39 -0500
Subject: [PATCH] cmd/utils, cmd/geth: add --memorylimit flag

---
 cmd/geth/main.go   |  1 +
 cmd/utils/flags.go | 18 ++++++++++++++----
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/cmd/geth/main.go b/cmd/geth/main.go
index 0108867f5a..b5802f51e7 100644
--- a/cmd/geth/main.go
+++ b/cmd/geth/main.go
@@ -101,6 +101,7 @@ var (
 		utils.CachePreimagesFlag,
 		utils.CacheLogSizeFlag,
 		utils.FDLimitFlag,
+		utils.MemoryLimitFlag,
 		utils.CryptoKZGFlag,
 		utils.ListenPortFlag,
 		utils.DiscoveryPortFlag,
diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index 3a7360359d..8cd0658004 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -554,6 +554,11 @@ var (
 		Usage:    "Raise the open file descriptor resource limit (default = system fd limit)",
 		Category: flags.PerfCategory,
 	}
+	MemoryLimitFlag = &cli.IntFlag{
+		Name:     "memorylimit",
+		Usage:    "Soft memory limit for the Go runtime in megabytes (default = derived from --cache and available memory)",
+		Category: flags.PerfCategory,
+	}
 	CryptoKZGFlag = &cli.StringFlag{
 		Name:     "crypto.kzg",
 		Usage:    "KZG library implementation to use; gokzg (recommended) or ckzg",
@@ -1776,11 +1781,16 @@ func SetEthConfig(ctx *cli.Context, stack *node.Node, cfg *ethconfig.Config) {
 	// memory below a soft cap. We size the cap from the same cgroup-aware
 	// limit used for the cache sanitizer above (total), so it's large enough
 	// that GOGC=100 governs steady state but the limit engages under real
-	// memory pressure. When the effective limit can't be determined, leave
-	// Go's defaults untouched.
-	if total > 0 {
+	// memory pressure. An explicit --memorylimit overrides this and when neither
+	// is available, Go's defaults are left untouched.
+	if ctx.IsSet(MemoryLimitFlag.Name) {
+		memLimit := int64(ctx.Int(MemoryLimitFlag.Name)) * 1024 * 1024
+		log.Debug("Setting Go memory limit", "MB", memLimit/1024/1024, "source", "flag")
+		godebug.SetMemoryLimit(memLimit)
+		godebug.SetGCPercent(100)
+	} else if total > 0 {
 		cache := int64(ctx.Int(CacheFlag.Name)) * 1024 * 1024
-		// Target ~4× the cache so GOGC=100 governs steady state, but cap at
+		// Target ~4x the cache so GOGC=100 governs steady state, but cap at
 		// half of memory. The rest is for the OS, page cache, and off-heap
 		// caches like Pebble that SetMemoryLimit doesn't count.
 		memLimit := min(int64(total)/2, cache*4)