doc/news.texi |  8 ++++++++
 ifchange.go   |  5 +++--
 main.go       | 56 +++++++++++++++++++++++++++++++++++++++++++++++++----
 ood.go        | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 run.go        |  7 +++++++
 usage.go      |  2 +-

diff --git a/doc/news.texi b/doc/news.texi
index ad51e4de56436a19cb80abbdc2c665ee5fb913811dd003d85833c909c80dce0e..beaeb9e4414063d295a98db03a5877ff459ad142c2f12562e0c7ddadb31780cb 100644
--- a/doc/news.texi
+++ b/doc/news.texi
@@ -1,6 +1,14 @@
 @node News
 @unnumbered News
 
+@anchor{Release 1.3.0}
+@section Release 1.3.0
+@itemize
+@item
+    Repetitive OOD determination optimization: pass all already known to
+    be OOD targets to redoing targets.
+@end itemize
+
 @anchor{Release 1.2.0}
 @section Release 1.2.0
 @itemize
diff --git a/ifchange.go b/ifchange.go
index 6f8593832a9fdc72593f104ac17fb02c85e6049fc10e03bd5afd88c136356f71..733718932353675ad0d2baefd3deaf132b162da23a5cfd0b13adf83f3e4359c9 100644
--- a/ifchange.go
+++ b/ifchange.go
@@ -139,7 +139,7 @@ 	errs = make(chan error, len(queue))
 	jobs := 0
 	queueSrc = []string{}
 	for _, tgt := range queue {
-		ood, err := isOOD(Cwd, tgt, 0, seen)
+		ood, err := isOODWithTrace(Cwd, tgt, 0, seen)
 		if err != nil {
 			trace(CErr, "dependant error: %s, skipping dependants", err)
 			return nil
@@ -176,6 +176,7 @@ 	jsInit()
 	defer jsAcquire("ifchange exiting")
 	defer Jobs.Wait()
 	seen := buildDependants(tgts)
+	oodTgtsClear()
 	trace(CDebug, "building %d targets: %v", len(tgts), tgts)
 	jobs := 0
 	errs := make(chan error, len(tgts))
@@ -188,7 +189,7 @@ 			continue
 		}
 		ood = true
 		if !forced {
-			ood, err = isOOD(Cwd, tgt, 0, seen)
+			ood, err = isOODWithTrace(Cwd, tgt, 0, seen)
 			if err != nil {
 				return false, err
 			}
diff --git a/main.go b/main.go
index 2ba9e6da15e77a7ca7a8644a0c31124eb178f1dfd2c38ade0351f2292af60347..b7d5ad6a75b8b149dcf929477c5241d393de12dbe5f9eaeff7fcf86f6de0f7bb 100644
--- a/main.go
+++ b/main.go
@@ -18,6 +18,8 @@
 package main
 
 import (
+	"bufio"
+	"bytes"
 	"crypto/rand"
 	"flag"
 	"fmt"
@@ -30,6 +32,7 @@ 	"path/filepath"
 	"strconv"
 
 	"go.cypherpunks.ru/recfile"
+	"golang.org/x/sys/unix"
 )
 
 var (
@@ -159,6 +162,46 @@ 		traced = os.Getenv(EnvTrace) == "1"
 	}
 
 	// Those are internal envs
+	FdOODTgts, err = ioutil.TempFile("", "ood-tgts")
+	if err != nil {
+		panic(err)
+	}
+	if err = os.Remove(FdOODTgts.Name()); err != nil {
+		panic(err)
+	}
+	FdOODTgtsLock, err = ioutil.TempFile("", "ood-tgts.lock")
+	if err != nil {
+		panic(err)
+	}
+	if err = os.Remove(FdOODTgtsLock.Name()); err != nil {
+		panic(err)
+	}
+
+	if v := os.Getenv(EnvOODTgtsFd); v != "" {
+		fd := mustParseFd(v, EnvOODTgtsFd)
+		fdLock := mustParseFd(v, EnvOODTgtsLockFd)
+		if err = unix.Flock(int(fdLock.Fd()), unix.LOCK_EX); err != nil {
+			panic(err)
+		}
+		if _, err = fd.Seek(0, os.SEEK_SET); err != nil {
+			panic(err)
+		}
+		tgtsRaw, err := ioutil.ReadAll(bufio.NewReader(fd))
+		if err != nil {
+			panic(err)
+		}
+		unix.Flock(int(fdLock.Fd()), unix.LOCK_UN)
+		OODTgts = make(map[string]struct{})
+		for _, tgtRaw := range bytes.Split(tgtsRaw, []byte{0}) {
+			t := string(tgtRaw)
+			if t == "" {
+				continue
+			}
+			OODTgts[t] = struct{}{}
+			trace(CDebug, "ood: known to be: %s", t)
+		}
+	}
+
 	StderrPrefix = os.Getenv(EnvStderrPrefix)
 	if v := os.Getenv(EnvLevel); v != "" {
 		Level, err = strconv.Atoi(v)
@@ -169,12 +212,14 @@ 		if Level < 0 {
 			panic("negative " + EnvLevel)
 		}
 	}
+
 	var fdDep *os.File
 	if v := os.Getenv(EnvDepFd); v != "" {
 		fdDep = mustParseFd(v, EnvDepFd)
 	}
+
+	tgts := flag.Args()
 	BuildUUID = os.Getenv(EnvBuildUUID)
-	tgts := flag.Args()
 	if BuildUUID == "" {
 		raw := new([16]byte)
 		if _, err = io.ReadFull(rand.Reader, raw[:]); err != nil {
@@ -189,6 +234,7 @@ 		if len(tgts) == 0 {
 			tgts = []string{"all"}
 		}
 	}
+
 	statusInit()
 
 	for i, tgt := range tgts {
@@ -264,17 +310,19 @@ 		if len(tgts) != 1 {
 			log.Fatalln("single target expected")
 		}
 		var fdTmp *os.File
-		fdTmp, err = ioutil.TempFile("", "")
+		fdTmp, err = ioutil.TempFile("", "whichdo")
 		if err != nil {
 			break
 		}
-		os.Remove(fdTmp.Name())
+		if err = os.Remove(fdTmp.Name()); err != nil {
+			break
+		}
 		cwd, tgt := cwdAndTgt(tgts[0])
 		doFile, upLevels, err := findDo(fdTmp, cwd, tgt)
 		if err != nil {
 			break
 		}
-		_, err = fdTmp.Seek(0, 0)
+		_, err = fdTmp.Seek(0, os.SEEK_SET)
 		if err != nil {
 			break
 		}
diff --git a/ood.go b/ood.go
index ca7e38fcca1b08dc8a9d9fa566141c4db59784c09ecccf5ec7c4993088b274e9..c20753526687484c72c7f561569ca985681fbbc671df94b6a8c6c32aca3d2238 100644
--- a/ood.go
+++ b/ood.go
@@ -26,6 +26,8 @@ 	"os"
 	"path"
 	"path/filepath"
 	"strings"
+
+	"golang.org/x/sys/unix"
 )
 
 const (
@@ -33,6 +35,15 @@ 	DepTypeIfcreate = "ifcreate"
 	DepTypeIfchange = "ifchange"
 	DepTypeAlways   = "always"
 	DepTypeStamp    = "stamp"
+
+	EnvOODTgtsFd     = "REDO_OOD_TGTS_FD"
+	EnvOODTgtsLockFd = "REDO_OOD_TGTS_LOCK_FD"
+)
+
+var (
+	OODTgts       map[string]struct{}
+	FdOODTgts     *os.File
+	FdOODTgtsLock *os.File
 )
 
 type TgtErr struct {
@@ -170,7 +181,7 @@ 			trace(CDebug, "ood: %s%s -> %s: was always built", indent, tgtOrig, dep)
 			continue
 		}
 
-		depOod, err := isOOD(cwd, dep, level+1, seen)
+		depOod, err := isOODWithTrace(cwd, dep, level+1, seen)
 		if err != nil {
 			return ood, TgtErr{tgtOrig, err}
 		}
@@ -186,3 +197,49 @@ Done:
 	trace(CDebug, "ood: %s%s: %v", indent, tgtOrig, ood)
 	return ood, nil
 }
+
+func isOODWithTrace(
+	cwd, tgtOrig string,
+	level int,
+	seen map[string]struct{},
+) (bool, error) {
+	p, err := filepath.Abs(path.Join(cwd, tgtOrig))
+	if err != nil {
+		panic(err)
+	}
+	_, ood := OODTgts[p]
+	if ood {
+		trace(
+			CDebug,
+			"ood: %s%s true, external decision",
+			strings.Repeat(". ", level), tgtOrig,
+		)
+		goto RecordOODTgt
+	}
+	ood, err = isOOD(cwd, tgtOrig, level, seen)
+	if !ood {
+		return ood, err
+	}
+RecordOODTgt:
+	if err = unix.Flock(int(FdOODTgtsLock.Fd()), unix.LOCK_EX); err != nil {
+		panic(err)
+	}
+	if _, err = FdOODTgts.Seek(0, os.SEEK_END); err != nil {
+		panic(err)
+	}
+	if _, err := FdOODTgts.WriteString(p + "\x00"); err != nil {
+		panic(err)
+	}
+	unix.Flock(int(FdOODTgtsLock.Fd()), unix.LOCK_UN)
+	return true, nil
+}
+
+func oodTgtsClear() {
+	if err := unix.Flock(int(FdOODTgtsLock.Fd()), unix.LOCK_EX); err != nil {
+		panic(err)
+	}
+	if err := FdOODTgts.Truncate(0); err != nil {
+		panic(err)
+	}
+	unix.Flock(int(FdOODTgtsLock.Fd()), unix.LOCK_UN)
+}
diff --git a/run.go b/run.go
index bb231dda450131a578ea4dfa3970dd8e16253ed9e97038ef1b15e65bb09b3a2c..fcaa2fb355dd2e8ad3b1876eb56e35ffba2ed28869a8d615d47b4477da402927 100644
--- a/run.go
+++ b/run.go
@@ -345,6 +345,13 @@ 		"%s=%s", EnvStderrPrefix, childStderrPrefix,
 	))
 
 	fdNum := 0
+	cmd.ExtraFiles = append(cmd.ExtraFiles, FdOODTgts)
+	cmd.Env = append(cmd.Env, fmt.Sprintf("%s=%d", EnvOODTgtsFd, 3+fdNum))
+	fdNum++
+	cmd.ExtraFiles = append(cmd.ExtraFiles, FdOODTgtsLock)
+	cmd.Env = append(cmd.Env, fmt.Sprintf("%s=%d", EnvOODTgtsLockFd, 3+fdNum))
+	fdNum++
+
 	if FdStatus == nil {
 		cmd.Env = append(cmd.Env, fmt.Sprintf("%s=NO", EnvStatusFd))
 	} else {
diff --git a/usage.go b/usage.go
index 9ad49630f9fcc208b71e627f90725ce1f53a56f93133dd42433b75e41d0306a4..1945e50184702b4b87a4d02a205161c772e996f7ec0850e609d2a250ff859b63 100644
--- a/usage.go
+++ b/usage.go
@@ -26,7 +26,7 @@ 	"strings"
 )
 
 const (
-	Version  = "1.2.0"
+	Version  = "1.3.0"
 	Warranty = `This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, version 3 of the License.