Revert "Return back pools segementation by size".

This reverts commit 08eb8e13d0,
since it led to high memory usage on the production box.

The commit need additional investigation.

pool.go

@@ -18,36 +18,28 @@ const (
 )
 
 type byteBufferPool struct {
+	calls       [steps]uint64
 	calibrating uint64
 
 	defaultSize uint64
 	maxSize     uint64
 
-	calls [steps]uint64
-	idxs  [steps]uint64
-	pools [steps]sync.Pool
+	pool sync.Pool
 }
 
 func (p *byteBufferPool) Acquire() *ByteBuffer {
-	for i := 0; i < steps; i++ {
-		idx := atomic.LoadUint64(&p.idxs[i])
-		if idx >= steps {
-			break
-		}
-		v := p.pools[idx].Get()
-		if v != nil {
-			return v.(*ByteBuffer)
-		}
+	v := p.pool.Get()
+	if v != nil {
+		return v.(*ByteBuffer)
 	}
-
 	return &ByteBuffer{
 		B: make([]byte, 0, atomic.LoadUint64(&p.defaultSize)),
 	}
 }
 
 func (p *byteBufferPool) Release(b *ByteBuffer) {
-	bLen := uint64(len(b.B))
-	idx := index(bLen)
+	bSize := len(b.B)
+	idx := bitSize(bSize-1) - minBitSize
 	if idx < 0 {
 		idx = 0
 	} else if idx >= steps {
@@ -58,12 +50,10 @@ func (p *byteBufferPool) Release(b *ByteBuffer) {
 		p.calibrate()
 	}
 
-	maxSize := atomic.LoadUint64(&p.maxSize)
-	bCap := uint64(cap(b.B))
-	if maxSize > 0 && bCap <= maxSize {
-		idx = index(bCap)
+	maxSize := int(atomic.LoadUint64(&p.maxSize))
+	if maxSize > 0 && bSize <= maxSize {
 		b.B = b.B[:0]
-		p.pools[idx].Put(b)
+		p.pool.Put(b)
 	}
 }
 
@@ -90,16 +80,14 @@ func (p *byteBufferPool) calibrate() {
 	maxSum := uint64(float64(callsSum) * maxPercentile)
 	callsSum = 0
 	for i := 0; i < steps; i++ {
-		idx := uint64(steps)
-		if callsSum <= maxSum {
-			callsSum += a[i].calls
-			size := a[i].size
-			if size > maxSize {
-				maxSize = size
-			}
-			idx = index(size)
+		if callsSum > maxSum {
+			break
+		}
+		callsSum += a[i].calls
+		size := a[i].size
+		if size > maxSize {
+			maxSize = size
 		}
-		atomic.StoreUint64(&p.idxs[i], idx)
 	}
 
 	atomic.StoreUint64(&p.defaultSize, defaultSize)
@@ -127,12 +115,8 @@ func (ci callSizes) Swap(i, j int) {
 	ci[i], ci[j] = ci[j], ci[i]
 }
 
-func index(n uint64) uint64 {
-	return bitSize(n-1) - minBitSize
-}
-
-func bitSize(n uint64) uint64 {
-	s := uint64(0)
+func bitSize(n int) int {
+	s := 0
 	for n > 0 {
 		n >>= 1
 		s++