@@ -13,11 +13,13 @@ import (

 	"github.com/docker/docker/api/types"

 	"github.com/docker/docker/api/types/backend"

 	"github.com/docker/docker/builder"

+	"github.com/docker/docker/daemon/config"

 	"github.com/docker/docker/daemon/images"

 	"github.com/docker/docker/pkg/streamformatter"

 	"github.com/docker/docker/pkg/system"

 	"github.com/docker/libnetwork"

 	controlapi "github.com/moby/buildkit/api/services/control"

+	"github.com/moby/buildkit/client"

 	"github.com/moby/buildkit/control"

 	"github.com/moby/buildkit/identity"

 	"github.com/moby/buildkit/session"

@@ -57,6 +59,7 @@ type Opt struct {

 	NetworkController   libnetwork.NetworkController

 	DefaultCgroupParent string

 	ResolverOpt         resolver.ResolveOptionsFunc

+	BuilderConfig       config.BuilderConfig

 }

 // Builder can build using BuildKit backend

@@ -134,43 +137,18 @@ func (b *Builder) Prune(ctx context.Context, opts types.BuildCachePruneOptions)

 		return 0, nil, err

 	}

-	var unusedFor time.Duration

-	unusedForValues := opts.Filters.Get("unused-for")

-

-	switch len(unusedForValues) {

-	case 0:

-

-	case 1:

-		var err error

-		unusedFor, err = time.ParseDuration(unusedForValues[0])

-		if err != nil {

-			return 0, nil, errors.Wrap(err, "unused-for filter expects a duration (e.g., '24h')")

-		}

-

-	default:

-		return 0, nil, errMultipleFilterValues

-	}

-

-	bkFilter := make([]string, 0, opts.Filters.Len())

-	for cacheField := range cacheFields {

-		values := opts.Filters.Get(cacheField)

-		switch len(values) {

-		case 0:

-			bkFilter = append(bkFilter, cacheField)

-		case 1:

-			bkFilter = append(bkFilter, cacheField+"=="+values[0])

-		default:

-			return 0, nil, errMultipleFilterValues

-		}

+	pi, err := toBuildkitPruneInfo(opts)

+	if err != nil {

+		return 0, nil, err

 	}

 	eg.Go(func() error {

 		defer close(ch)

 		return b.controller.Prune(&controlapi.PruneRequest{

-			All:          opts.All,

-			KeepDuration: int64(unusedFor),

-			KeepBytes:    opts.KeepStorage,

-			Filter:       bkFilter,

+			All:          pi.All,

+			KeepDuration: int64(pi.KeepDuration),

+			KeepBytes:    pi.KeepBytes,

+			Filter:       pi.Filter,

 		}, &pruneProxy{

 			streamProxy: streamProxy{ctx: ctx},

 			ch:          ch,

@@ -531,3 +509,41 @@ func toBuildkitExtraHosts(inp []string) (string, error) {

 	}

 	return strings.Join(hosts, ","), nil

 }

+

+func toBuildkitPruneInfo(opts types.BuildCachePruneOptions) (client.PruneInfo, error) {

+	var unusedFor time.Duration

+	unusedForValues := opts.Filters.Get("unused-for")

+

+	switch len(unusedForValues) {

+	case 0:

+

+	case 1:

+		var err error

+		unusedFor, err = time.ParseDuration(unusedForValues[0])

+		if err != nil {

+			return client.PruneInfo{}, errors.Wrap(err, "unused-for filter expects a duration (e.g., '24h')")

+		}

+

+	default:

+		return client.PruneInfo{}, errMultipleFilterValues

+	}

+

+	bkFilter := make([]string, 0, opts.Filters.Len())

+	for cacheField := range cacheFields {

+		values := opts.Filters.Get(cacheField)

+		switch len(values) {

+		case 0:

+			bkFilter = append(bkFilter, cacheField)

+		case 1:

+			bkFilter = append(bkFilter, cacheField+"=="+values[0])

+		default:

+			return client.PruneInfo{}, errMultipleFilterValues

+		}

+	}

+	return client.PruneInfo{

+		All:          opts.All,

+		KeepDuration: unusedFor,

+		KeepBytes:    opts.KeepStorage,

+		Filter:       bkFilter,

+	}, nil

+}

@@ -6,15 +6,19 @@ import (

 	"path/filepath"

 	"github.com/containerd/containerd/content/local"

+	"github.com/docker/docker/api/types"

 	"github.com/docker/docker/builder/builder-next/adapters/containerimage"

 	"github.com/docker/docker/builder/builder-next/adapters/snapshot"

 	containerimageexp "github.com/docker/docker/builder/builder-next/exporter"

 	"github.com/docker/docker/builder/builder-next/imagerefchecker"

 	mobyworker "github.com/docker/docker/builder/builder-next/worker"

+	"github.com/docker/docker/daemon/config"

 	"github.com/docker/docker/daemon/graphdriver"

+	units "github.com/docker/go-units"

 	"github.com/moby/buildkit/cache"

 	"github.com/moby/buildkit/cache/metadata"

 	registryremotecache "github.com/moby/buildkit/cache/remotecache/registry"

+	"github.com/moby/buildkit/client"

 	"github.com/moby/buildkit/control"

 	"github.com/moby/buildkit/exporter"

 	"github.com/moby/buildkit/frontend"

@@ -127,12 +131,18 @@ func newController(rt http.RoundTripper, opt Opt) (*control.Controller, error) {

 		return nil, err

 	}

+	gcPolicy, err := getGCPolicy(opt.BuilderConfig, root)

+	if err != nil {

+		return nil, errors.Wrap(err, "could not get builder GC policy")

+	}

+

 	wopt := mobyworker.Opt{

 		ID:                "moby",

 		SessionManager:    opt.SessionManager,

 		MetadataStore:     md,

 		ContentStore:      store,

 		CacheManager:      cm,

+		GCPolicy:          gcPolicy,

 		Snapshotter:       snapshotter,

 		Executor:          exec,

 		ImageSource:       src,

@@ -165,3 +175,44 @@ func newController(rt http.RoundTripper, opt Opt) (*control.Controller, error) {

 		// TODO: set ResolveCacheExporterFunc for exporting cache

 	})

 }

+

+func getGCPolicy(conf config.BuilderConfig, root string) ([]client.PruneInfo, error) {

+	var gcPolicy []client.PruneInfo

+	if conf.GC.Enabled {

+		var (

+			defaultKeepStorage int64

+			err                error

+		)

+

+		if conf.GC.DefaultKeepStorage != "" {

+			defaultKeepStorage, err = units.RAMInBytes(conf.GC.DefaultKeepStorage)

+			if err != nil {

+				return nil, errors.Wrapf(err, "could not parse '%s' as Builder.GC.DefaultKeepStorage config", conf.GC.DefaultKeepStorage)

+			}

+		}

+

+		if conf.GC.Policy == nil {

+			gcPolicy = mobyworker.DefaultGCPolicy(root, defaultKeepStorage)

+		} else {

+			gcPolicy = make([]client.PruneInfo, len(conf.GC.Policy))

+			for i, p := range conf.GC.Policy {

+				b, err := units.RAMInBytes(p.KeepStorage)

+				if err != nil {

+					return nil, err

+				}

+				if b == 0 {

+					b = defaultKeepStorage

+				}

+				gcPolicy[i], err = toBuildkitPruneInfo(types.BuildCachePruneOptions{

+					All:         p.All,

+					KeepStorage: b,

+					Filters:     p.Filter,

+				})

+				if err != nil {

+					return nil, err

+				}

+			}

+		}

+	}

+	return gcPolicy, nil

+}

new file mode 100644

@@ -0,0 +1,51 @@

+package worker

+

+import (

+	"math"

+

+	"github.com/moby/buildkit/client"

+)

+

+const defaultCap int64 = 2e9 // 2GB

+

+// tempCachePercent represents the percentage ratio of the cache size in bytes to temporarily keep for a short period of time (couple of days)

+// over the total cache size in bytes. Because there is no perfect value, a mathematically pleasing one was chosen.

+// The value is approximately 13.8

+const tempCachePercent = math.E * math.Pi * math.Phi

+

+// DefaultGCPolicy returns a default builder GC policy

+func DefaultGCPolicy(p string, defaultKeepBytes int64) []client.PruneInfo {

+	keep := defaultKeepBytes

+	if defaultKeepBytes == 0 {

+		keep = detectDefaultGCCap(p)

+	}

+

+	tempCacheKeepBytes := int64(math.Round(float64(keep) / 100. * float64(tempCachePercent)))

+	const minTempCacheKeepBytes = 512 * 1e6 // 512MB

+	if tempCacheKeepBytes < minTempCacheKeepBytes {

+		tempCacheKeepBytes = minTempCacheKeepBytes

+	}

+

+	return []client.PruneInfo{

+		// if build cache uses more than 512MB delete the most easily reproducible data after it has not been used for 2 days

+		{

+			Filter:       []string{"type==source.local,type==exec.cachemount,type==source.git.checkout"},

+			KeepDuration: 48 * 3600, // 48h

+			KeepBytes:    tempCacheKeepBytes,

+		},

+		// remove any data not used for 60 days

+		{

+			KeepDuration: 60 * 24 * 3600, // 60d

+			KeepBytes:    keep,

+		},

+		// keep the unshared build cache under cap

+		{

+			KeepBytes: keep,

+		},

+		// if previous policies were insufficient start deleting internal data to keep build cache under cap

+		{

+			All:       true,

+			KeepBytes: keep,

+		},

+	}

+}

new file mode 100644

@@ -0,0 +1,17 @@

+// +build !windows

+

+package worker

+

+import (

+	"syscall"

+)

+

+func detectDefaultGCCap(root string) int64 {

+	var st syscall.Statfs_t

+	if err := syscall.Statfs(root, &st); err != nil {

+		return defaultCap

+	}

+	diskSize := int64(st.Bsize) * int64(st.Blocks) // nolint unconvert

+	avail := diskSize / 10

+	return (avail/(1<<30) + 1) * 1e9 // round up

+}

new file mode 100644

@@ -0,0 +1,7 @@

+// +build windows

+

+package worker

+

+func detectDefaultGCCap(root string) int64 {

+	return defaultCap

+}

@@ -292,6 +292,7 @@ func newRouterOptions(config *config.Config, d *daemon.Daemon) (routerOptions, e

 		NetworkController:   d.NetworkController(),

 		DefaultCgroupParent: cgroupParent,

 		ResolverOpt:         d.NewResolveOptionsFunc(),

+		BuilderConfig:       config.Builder,

 	})

 	if err != nil {

 		return opts, err

new file mode 100644

@@ -0,0 +1,22 @@

+package config

+

+import "github.com/docker/docker/api/types/filters"

+

+// BuilderGCRule represents a GC rule for buildkit cache

+type BuilderGCRule struct {

+	All         bool         `json:",omitempty"`

+	Filter      filters.Args `json:",omitempty"`

+	KeepStorage string       `json:",omitempty"`

+}

+

+// BuilderGCConfig contains GC config for a buildkit builder

+type BuilderGCConfig struct {

+	Enabled            bool            `json:",omitempty"`

+	Policy             []BuilderGCRule `json:",omitempty"`

+	DefaultKeepStorage string          `json:",omitempty"`

+}

+

+// BuilderConfig contains config for the builder

+type BuilderConfig struct {

+	GC BuilderGCConfig `json:",omitempty"`

+}

@@ -55,6 +55,7 @@ var flatOptions = map[string]bool{

 	"runtimes":           true,

 	"default-ulimits":    true,

 	"features":           true,

+	"builder":            true,

 }

 // skipValidateOptions contains configuration keys

@@ -62,6 +63,7 @@ var flatOptions = map[string]bool{

 // for unknown flag validation.

 var skipValidateOptions = map[string]bool{

 	"features": true,

+	"builder":  true,

 }

 // skipDuplicates contains configuration keys that

@@ -225,6 +227,8 @@ type CommonConfig struct {

 	// Features contains a list of feature key value pairs indicating what features are enabled or disabled.

 	// If a certain feature doesn't appear in this list then it's unset (i.e. neither true nor false).

 	Features map[string]bool `json:"features,omitempty"`

+

+	Builder BuilderConfig `json:"builder,omitempty"`

 }

 // IsValueSet returns true if a configuration value