fix memory allocation

weed/util/mem/slot_pool.go

@@ -14,7 +14,7 @@ const (
 
 func bitCount(size int) (count int) {
 	for ; size > min_size; count++ {
-		size = size >> 1
+		size = (size + 1) >> 1
 	}
 	return
 }

weed/util/mem/slot_pool_test.go

@@ -1,6 +1,7 @@
 package mem
 
 import (
+	"github.com/stretchr/testify/assert"
 	"testing"
 )
 
@@ -25,6 +26,16 @@ func TestAllocateFree(t *testing.T) {
 
 }
 
+func TestAllocateFreeEdgeCases(t *testing.T) {
+	assert.Equal(t, 1, bitCount(2048))
+	assert.Equal(t, 2, bitCount(2049))
+
+	buf := Allocate(2048)
+	Free(buf)
+	buf = Allocate(2049)
+	Free(buf)
+}
+
 func TestBitCount(t *testing.T) {
 	count := bitCount(12)
 	if count != 0 {