diff --git a/app/api/api.go b/app/api/api.go
index 73e48d8b..bd5b7cf5 100644
--- a/app/api/api.go
+++ b/app/api/api.go
@@ -847,6 +847,7 @@ func (a *api) start(ctx context.Context) error {
 				"type": "mem",
 				"name": "mem",
 			}),
+			Storage: "swiss",
 		}
 		var memfs fs.Filesystem = nil
 		if len(cfg.Storage.Memory.Backup.Dir) != 0 {
diff --git a/io/fs/mem.go b/io/fs/mem.go
index 2cc51637..e1d33aae 100644
--- a/io/fs/mem.go
+++ b/io/fs/mem.go
@@ -105,8 +105,10 @@ func (f *memFile) Seek(offset int64, whence int) (int64, error) {
 }
 
 func (f *memFile) Close() error {
+	var err error = nil
+
 	if f.r == nil {
-		return io.EOF
+		err = io.EOF
 	}
 
 	f.r = nil
@@ -116,7 +118,7 @@ func (f *memFile) Close() error {
 		f.data = nil
 	}
 
-	return nil
+	return err
 }
 
 type memFilesystem struct {
diff --git a/io/fs/memtest/memtest.go b/io/fs/memtest/memtest.go
index 771eb454..73828e6e 100644
--- a/io/fs/memtest/memtest.go
+++ b/io/fs/memtest/memtest.go
@@ -29,8 +29,9 @@ func main() {
 	oFiles := 15
 	oInterval := 1 // seconds
 	oSize := 2     // megabytes
-	oLimit := false
+	oLimit := -1
 	oGC := 0
+	oFree := 0
 
 	flag.StringVar(&oStorage, "storage", "mapof", "type of mem storage implementation (mapof, map, swiss)")
 	flag.IntVar(&oWriters, "writers", 500, "number of concurrent writers")
@@ -38,8 +39,9 @@ func main() {
 	flag.IntVar(&oFiles, "files", 15, "number of files to keep per writer")
 	flag.IntVar(&oInterval, "interval", 1, "interval for writing files in seconds")
 	flag.IntVar(&oSize, "size", 2048, "size of files to write in kilobytes")
-	flag.BoolVar(&oLimit, "limit", false, "set memory limit")
-	flag.IntVar(&oGC, "gc", 0, "force garbage collector")
+	flag.IntVar(&oLimit, "limit", -1, "set memory limit, 0 for automatic, otherwise memory in MB")
+	flag.IntVar(&oGC, "gc", 100, "GC percentage")
+	flag.IntVar(&oFree, "free", 0, "force freeing memory")
 
 	flag.Parse()
 
@@ -47,9 +49,14 @@ func main() {
 
 	fmt.Printf("Expecting effective memory consumption of %.1fGB\n", estimatedSize)
 
-	if oLimit {
-		fmt.Printf("Setting memory limit to %.1fGB\n", estimatedSize*1.5)
-		debug.SetMemoryLimit(int64(estimatedSize * 1.5))
+	if oLimit >= 0 {
+		limitSize := estimatedSize * 1.5 * 1024 * 1024 * 1024
+		if oLimit > 0 {
+			limitSize = float64(oLimit) * 1024 * 1024
+		}
+
+		fmt.Printf("Setting memory limit to %.1fGB\n", limitSize/1024/1024/1024)
+		debug.SetMemoryLimit(int64(limitSize))
 	}
 
 	memfs, err := fs.NewMemFilesystem(fs.MemConfig{
@@ -206,9 +213,11 @@ func main() {
 		}
 	}(ctx, memfs)
 
-	if oGC > 0 {
+	debug.SetGCPercent(oGC)
+
+	if oFree > 0 {
 		go func(ctx context.Context) {
-			ticker := time.NewTicker(time.Duration(oGC) * time.Second)
+			ticker := time.NewTicker(time.Duration(oFree) * time.Second)
 			defer ticker.Stop()
 
 			for {
diff --git a/mem/pool_test.go b/mem/pool_test.go
new file mode 100644
index 00000000..c194536c
--- /dev/null
+++ b/mem/pool_test.go
@@ -0,0 +1,94 @@
+package mem
+
+import (
+	"math/rand"
+	"testing"
+	"time"
+)
+
+func TestIndex(t *testing.T) {
+	testIndex(t, 0, 0)
+	testIndex(t, 1, 0)
+
+	testIndex(t, minSize-1, 0)
+	testIndex(t, minSize, 0)
+	testIndex(t, minSize+1, 1)
+
+	testIndex(t, 2*minSize-1, 1)
+	testIndex(t, 2*minSize, 1)
+	testIndex(t, 2*minSize+1, 2)
+
+	testIndex(t, maxSize-1, steps-1)
+	testIndex(t, maxSize, steps-1)
+	testIndex(t, maxSize+1, steps-1)
+}
+
+func testIndex(t *testing.T, n, expectedIdx int) {
+	idx := index(n)
+	if idx != expectedIdx {
+		t.Fatalf("unexpected idx for n=%d: %d. Expecting %d", n, idx, expectedIdx)
+	}
+}
+
+func TestPoolCalibrate(t *testing.T) {
+	for i := 0; i < steps*calibrateCallsThreshold; i++ {
+		n := 1004
+		if i%15 == 0 {
+			n = rand.Intn(15234)
+		}
+		testGetPut(t, n)
+	}
+}
+
+func TestPoolVariousSizesSerial(t *testing.T) {
+	testPoolVariousSizes(t)
+}
+
+func TestPoolVariousSizesConcurrent(t *testing.T) {
+	concurrency := 5
+	ch := make(chan struct{})
+	for i := 0; i < concurrency; i++ {
+		go func() {
+			testPoolVariousSizes(t)
+			ch <- struct{}{}
+		}()
+	}
+	for i := 0; i < concurrency; i++ {
+		select {
+		case <-ch:
+		case <-time.After(3 * time.Second):
+			t.Fatalf("timeout")
+		}
+	}
+}
+
+func testPoolVariousSizes(t *testing.T) {
+	for i := 0; i < steps+1; i++ {
+		n := (1 << uint32(i))
+
+		testGetPut(t, n)
+		testGetPut(t, n+1)
+		testGetPut(t, n-1)
+
+		for j := 0; j < 10; j++ {
+			testGetPut(t, j+n)
+		}
+	}
+}
+
+func testGetPut(t *testing.T, n int) {
+	bb := Get()
+	if len(bb.data) > 0 {
+		t.Fatalf("non-empty byte buffer returned from acquire")
+	}
+	bb.data = allocNBytes(bb.data, n)
+	Put(bb)
+}
+
+func allocNBytes(dst []byte, n int) []byte {
+	diff := n - cap(dst)
+	if diff <= 0 {
+		return dst[:n]
+	}
+	return append(dst, make([]byte, diff)...)
+}