Merge pull request #12750 from ptabor/20210306-mlock

--experimental-memory-mlock support

server/etcdserver/config.go

@@ -169,6 +169,14 @@ type ServerConfig struct {
 	UnsafeNoFsync bool `json:"unsafe-no-fsync"`
 
 	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"`
 }
 
 // VerifyBootstrap sanity-checks the initial config for bootstrap case

server/etcdserver/mlock_not_unix.go

@@ -0,0 +1,27 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build windows
+// +build windows
+
+package etcdserver
+
+import (
+	"errors"
+)
+
+// MlockAll prevents current and future mmaped memory areas from being swapped out.
+func MlockAll() error {
+	return errors.New("Mlockall is supported only on UNIX systems.")
+}

server/etcdserver/mlock_unix.go

@@ -0,0 +1,33 @@
+// Copyright 2021 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || zos
+// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris zos
+
+package etcdserver
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/unix"
+)
+
+// MlockAll prevents current and future mmaped memory areas from being swapped out.
+func MlockAll() error {
+	err := unix.Mlockall(unix.MCL_FUTURE | unix.MCL_CURRENT)
+	if err != nil {
+		return fmt.Errorf("cannot mlockAll: %v", err)
+	}
+	return nil
+}

server/etcdserver/server.go

@@ -316,6 +316,14 @@ func NewServer(cfg ServerConfig) (srv *EtcdServer, err error) {
 		)
 	}
 
+	if cfg.ExperimentalMemoryMlock {
+		cfg.Logger.Info("mlocking memory")
+		err := MlockAll()
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	if terr := fileutil.TouchDirAll(cfg.DataDir); terr != nil {
 		return nil, fmt.Errorf("cannot access data directory: %v", terr)
 	}