vendor/github.com/coreos/etcd/mvcc/backend/config_linux.go

// Copyright 2015 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.

package backend

import (
	"syscall"

	bolt "github.com/coreos/bbolt"
)

// syscall.MAP_POPULATE on linux 2.6.23+ does sequential read-ahead
// which can speed up entire-database read with boltdb. We want to
// enable MAP_POPULATE for faster key-value store recovery in storage
// package. If your kernel version is lower than 2.6.23
// (https://github.com/torvalds/linux/releases/tag/v2.6.23), mmap might
// silently ignore this flag. Please update your kernel to prevent this.
var boltOpenOptions = &bolt.Options{
	MmapFlags:      syscall.MAP_POPULATE,
	NoFreelistSync: true,
}

func (bcfg *BackendConfig) mmapSize() int { return int(bcfg.MmapSize) }