Revert "migrate experimental-memory-mlock to feature gate"

This reverts commit 9d335cf.

server/config/config.go

@@ -22,14 +22,14 @@ import (
 	"strings"
 	"time"
 
+	"go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc"
+	"go.uber.org/zap"
+
 	bolt "go.etcd.io/bbolt"
 	"go.etcd.io/etcd/client/pkg/v3/transport"
 	"go.etcd.io/etcd/client/pkg/v3/types"
 	"go.etcd.io/etcd/pkg/v3/featuregate"
 	"go.etcd.io/etcd/pkg/v3/netutil"
-	"go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc"
-	"go.uber.org/zap"
-
 	"go.etcd.io/etcd/server/v3/etcdserver/api/v3discovery"
 	"go.etcd.io/etcd/server/v3/storage/datadir"
 )
@@ -184,6 +184,14 @@ type ServerConfig struct {
 
 	DowngradeCheckTime time.Duration
 
+	// ExperimentalMemoryMlock enables mlocking of etcd owned memory pages.
+	// The setting improves etcd tail latency in environments were:
+	//   - memory pressure might lead to swapping pages to disk
+	//   - disk latency might be unstable
+	// Currently all etcd memory gets mlocked, but in future the flag can
+	// be refined to mlock in-use area of bbolt only.
+	ExperimentalMemoryMlock bool `json:"experimental-memory-mlock"`
+
 	// ExperimentalTxnModeWriteWithSharedBuffer enable write transaction to use
 	// a shared buffer in its readonly check operations.
 	ExperimentalTxnModeWriteWithSharedBuffer bool `json:"experimental-txn-mode-write-with-shared-buffer"`

server/embed/config.go

@@ -30,6 +30,11 @@ import (
 	"sync"
 	"time"
 
+	"go.uber.org/zap"
+	"golang.org/x/crypto/bcrypt"
+	"google.golang.org/grpc"
+	"sigs.k8s.io/yaml"
+
 	bolt "go.etcd.io/bbolt"
 	"go.etcd.io/etcd/client/pkg/v3/logutil"
 	"go.etcd.io/etcd/client/pkg/v3/srv"
@@ -40,11 +45,6 @@ import (
 	"go.etcd.io/etcd/pkg/v3/featuregate"
 	"go.etcd.io/etcd/pkg/v3/flags"
 	"go.etcd.io/etcd/pkg/v3/netutil"
-	"go.uber.org/zap"
-	"golang.org/x/crypto/bcrypt"
-	"google.golang.org/grpc"
-	"sigs.k8s.io/yaml"
-
 	"go.etcd.io/etcd/server/v3/config"
 	"go.etcd.io/etcd/server/v3/etcdserver"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/membership"
@@ -477,8 +477,6 @@ type Config struct {
 	//   - disk latency might be unstable
 	// Currently all etcd memory gets mlocked, but in future the flag can
 	// be refined to mlock in-use area of bbolt only.
-	// Deprecated in v3.6 and will be decommissioned in v3.7.
-	// TODO: delete in v3.7
 	ExperimentalMemoryMlock bool `json:"experimental-memory-mlock"`
 
 	// ExperimentalTxnModeWriteWithSharedBuffer enables write transaction to use a shared buffer in its readonly check operations.
@@ -596,6 +594,7 @@ func NewConfig() *Config {
 		EnableGRPCGateway:     true,
 
 		ExperimentalDowngradeCheckTime:      DefaultDowngradeCheckTime,
+		ExperimentalMemoryMlock:             false,
 		ExperimentalStopGRPCServiceOnDefrag: false,
 		ExperimentalMaxLearners:             membership.DefaultMaxLearners,
 
@@ -803,7 +802,6 @@ func (cfg *Config) AddFlags(fs *flag.FlagSet) {
 	fs.DurationVar(&cfg.ExperimentalWarningApplyDuration, "experimental-warning-apply-duration", cfg.ExperimentalWarningApplyDuration, "Time duration after which a warning is generated if request takes more time.")
 	fs.DurationVar(&cfg.WarningUnaryRequestDuration, "warning-unary-request-duration", cfg.WarningUnaryRequestDuration, "Time duration after which a warning is generated if a unary request takes more time.")
 	fs.DurationVar(&cfg.ExperimentalWarningUnaryRequestDuration, "experimental-warning-unary-request-duration", cfg.ExperimentalWarningUnaryRequestDuration, "Time duration after which a warning is generated if a unary request takes more time. It's deprecated, and will be decommissioned in v3.7. Use --warning-unary-request-duration instead.")
-	// TODO: delete in v3.7
 	fs.BoolVar(&cfg.ExperimentalMemoryMlock, "experimental-memory-mlock", cfg.ExperimentalMemoryMlock, "Enable to enforce etcd pages (in particular bbolt) to stay in RAM.")
 	fs.BoolVar(&cfg.ExperimentalTxnModeWriteWithSharedBuffer, "experimental-txn-mode-write-with-shared-buffer", true, "Enable the write transaction to use a shared buffer in its readonly check operations.")
 	fs.BoolVar(&cfg.ExperimentalStopGRPCServiceOnDefrag, "experimental-stop-grpc-service-on-defrag", cfg.ExperimentalStopGRPCServiceOnDefrag, "Enable etcd gRPC service to stop serving client requests on defragmentation.")

server/embed/etcd.go

@@ -33,17 +33,17 @@ import (
 
 	grpc_prometheus "github.com/grpc-ecosystem/go-grpc-prometheus"
 	"github.com/soheilhy/cmux"
+	"go.uber.org/zap"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/keepalive"
+
 	"go.etcd.io/etcd/api/v3/version"
 	"go.etcd.io/etcd/client/pkg/v3/transport"
 	"go.etcd.io/etcd/client/pkg/v3/types"
 	"go.etcd.io/etcd/client/v3/credentials"
 	"go.etcd.io/etcd/pkg/v3/debugutil"
 	runtimeutil "go.etcd.io/etcd/pkg/v3/runtime"
-	"go.uber.org/zap"
-	"google.golang.org/grpc"
-	"google.golang.org/grpc/credentials/insecure"
-	"google.golang.org/grpc/keepalive"
-
 	"go.etcd.io/etcd/server/v3/config"
 	"go.etcd.io/etcd/server/v3/etcdserver"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/etcdhttp"
@@ -221,6 +221,7 @@ func StartEtcd(inCfg *Config) (e *Etcd, err error) {
 		DowngradeCheckTime:                   cfg.ExperimentalDowngradeCheckTime,
 		WarningApplyDuration:                 cfg.ExperimentalWarningApplyDuration,
 		WarningUnaryRequestDuration:          cfg.WarningUnaryRequestDuration,
+		ExperimentalMemoryMlock:              cfg.ExperimentalMemoryMlock,
 		ExperimentalBootstrapDefragThresholdMegabytes: cfg.ExperimentalBootstrapDefragThresholdMegabytes,
 		ExperimentalMaxLearners:                       cfg.ExperimentalMaxLearners,
 		V2Deprecation:                                 cfg.V2DeprecationEffective(),

server/etcdmain/help.go

@@ -313,7 +313,7 @@ Experimental feature:
     Duration of time between two downgrade status checks.
   --experimental-enable-lease-checkpoint-persist 'false'
     Enable persisting remainingTTL to prevent indefinite auto-renewal of long lived leases. Always enabled in v3.6. Should be used to ensure smooth upgrade from v3.5 clusters with this feature enabled. Requires experimental-enable-lease-checkpoint to be enabled.
-  --experimental-memory-mlock. Deprecated in v3.6 and will be decommissioned in v3.7. Use '--feature-gates=MemoryMlock=true' instead.
+  --experimental-memory-mlock
     Enable to enforce etcd pages (in particular bbolt) to stay in RAM.
   --experimental-snapshot-catchup-entries
     Number of entries for a slow follower to catch up after compacting the raft storage entries.

server/features/etcd_features.go

@@ -17,8 +17,9 @@ package features
 import (
 	"fmt"
 
-	"go.etcd.io/etcd/pkg/v3/featuregate"
 	"go.uber.org/zap"
+
+	"go.etcd.io/etcd/pkg/v3/featuregate"
 )
 
 const (
@@ -59,11 +60,6 @@ const (
 	// alpha: v3.6
 	// main PR: https://github.com/etcd-io/etcd/pull/14120
 	CompactHashCheck featuregate.Feature = "CompactHashCheck"
-	// MemoryMlock enforces etcd pages (in particular bbolt) to stay in RAM
-	// owner: @serathius
-	// alpha: v3.5
-	// main PR: https://github.com/etcd-io/etcd/pull/12750
-	MemoryMlock featuregate.Feature = "MemoryMlock"
 )
 
 var (
@@ -73,7 +69,6 @@ var (
 		InitialCorruptCheck:          {Default: false, PreRelease: featuregate.Alpha},
 		CompactHashCheck:             {Default: false, PreRelease: featuregate.Alpha},
 		TxnModeWriteWithSharedBuffer: {Default: true, PreRelease: featuregate.Beta},
-		MemoryMlock:                  {Default: false, PreRelease: featuregate.Alpha},
 	}
 	// ExperimentalFlagToFeatureMap is the map from the cmd line flags of experimental features
 	// to their corresponding feature gates.
@@ -83,7 +78,6 @@ var (
 		"experimental-initial-corrupt-check":             InitialCorruptCheck,
 		"experimental-compact-hash-check-enabled":        CompactHashCheck,
 		"experimental-txn-mode-write-with-shared-buffer": TxnModeWriteWithSharedBuffer,
-		"experimental-memory-mlock":                      MemoryMlock,
 	}
 )
 

server/storage/backend.go

@@ -19,14 +19,13 @@ import (
 	"os"
 	"time"
 
-	"go.etcd.io/raft/v3/raftpb"
 	"go.uber.org/zap"
 
 	"go.etcd.io/etcd/server/v3/config"
 	"go.etcd.io/etcd/server/v3/etcdserver/api/snap"
-	"go.etcd.io/etcd/server/v3/features"
 	"go.etcd.io/etcd/server/v3/storage/backend"
 	"go.etcd.io/etcd/server/v3/storage/schema"
+	"go.etcd.io/raft/v3/raftpb"
 )
 
 func newBackend(cfg config.ServerConfig, hooks backend.Hooks) backend.Backend {
@@ -51,7 +50,7 @@ func newBackend(cfg config.ServerConfig, hooks backend.Hooks) backend.Backend {
 		// permit 10% excess over quota for disarm
 		bcfg.MmapSize = uint64(cfg.QuotaBackendBytes + cfg.QuotaBackendBytes/10)
 	}
-	bcfg.Mlock = cfg.ServerFeatureGate.Enabled(features.MemoryMlock)
+	bcfg.Mlock = cfg.ExperimentalMemoryMlock
 	bcfg.Hooks = hooks
 	return backend.New(bcfg)
 }