// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: BUSL-1.1

//go:build linux

package cgroupslib

import (
	"sync"

	"github.com/hashicorp/nomad/helper/pointer"
)

var (
	disableMemorySwapOnce sync.Once
	disableMemorySwap     *uint64
)

// MaybeDisableMemorySwappiness will disable memory swappiness, if that controller
// is available. Always the case for cgroups v2, but is not always the case on
// very old kernels with cgroups v1.
func MaybeDisableMemorySwappiness() *uint64 {
	disableMemorySwapOnce.Do(func() {
		disableMemorySwap = detectMemorySwap()
	})
	return disableMemorySwap
}

func detectMemorySwap() *uint64 {
	switch GetMode() {
	case CG1:
		err := WriteNomadCG1("memory", "memory.swappiness", "0")
		if err == nil {
			return pointer.Of[uint64](0)
		}
		return nil
	default:
		return pointer.Of[uint64](0)
	}
}