diff --git a/cmd/geth/main.go b/cmd/geth/main.go
index 4f3849a41b7eb3159fcc1d703e95c90d3e3fbabd..c439e36fc0e6e9c893982c1eab1dc43eeaf5d2b2 100644
--- a/cmd/geth/main.go
+++ b/cmd/geth/main.go
@@ -234,6 +234,20 @@ func init() {
 		if err := debug.Setup(ctx, logdir); err != nil {
 			return err
 		}
+		// If we're a full node on mainnet without --cache specified, bump default cache allowance
+		if ctx.GlobalString(utils.SyncModeFlag.Name) != "light" && !ctx.GlobalIsSet(utils.CacheFlag.Name) && !ctx.GlobalIsSet(utils.NetworkIdFlag.Name) {
+			// Make sure we're not on any supported preconfigured testnet either
+			if !ctx.GlobalIsSet(utils.TestnetFlag.Name) && !ctx.GlobalIsSet(utils.RinkebyFlag.Name) && !ctx.GlobalIsSet(utils.GoerliFlag.Name) {
+				// Nope, we're really on mainnet. Bump that cache up!
+				log.Info("Bumping default cache on mainnet", "provided", ctx.GlobalInt(utils.CacheFlag.Name), "updated", 4096)
+				ctx.GlobalSet(utils.CacheFlag.Name, strconv.Itoa(4096))
+			}
+		}
+		// If we're running a light client on any network, drop the cache to some meaningfully low amount
+		if ctx.GlobalString(utils.SyncModeFlag.Name) == "light" && !ctx.GlobalIsSet(utils.CacheFlag.Name) {
+			log.Info("Dropping default light client cache", "provided", ctx.GlobalInt(utils.CacheFlag.Name), "updated", 128)
+			ctx.GlobalSet(utils.CacheFlag.Name, strconv.Itoa(128))
+		}
 		// Cap the cache allowance and tune the garbage collector
 		var mem gosigar.Mem
 		if err := mem.Get(); err == nil {
diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index f5f4cde5b433cc82dff26adef8c551dff1ce75d3..689202c6934d8e5c235fc562ff63672d8a239999 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -331,7 +331,7 @@ var (
 	// Performance tuning settings
 	CacheFlag = cli.IntFlag{
 		Name:  "cache",
-		Usage: "Megabytes of memory allocated to internal caching",
+		Usage: "Megabytes of memory allocated to internal caching (default = 4096 mainnet full node, 128 light mode)",
 		Value: 1024,
 	}
 	CacheDatabaseFlag = cli.IntFlag{