diff --git a/src/runtime/mksizeclasses.go b/src/runtime/mksizeclasses.go
index b4a117d343..8b9bbe01e6 100644
--- a/src/runtime/mksizeclasses.go
+++ b/src/runtime/mksizeclasses.go
@@ -37,6 +37,7 @@ import (
 	"go/format"
 	"io"
 	"log"
+	"math/bits"
 	"os"
 )
 
@@ -242,8 +243,9 @@ nextk:
 }
 
 func printComment(w io.Writer, classes []class) {
-	fmt.Fprintf(w, "// %-5s  %-9s  %-10s  %-7s  %-10s  %-9s\n", "class", "bytes/obj", "bytes/span", "objects", "tail waste", "max waste")
+	fmt.Fprintf(w, "// %-5s  %-9s  %-10s  %-7s  %-10s  %-9s  %-9s\n", "class", "bytes/obj", "bytes/span", "objects", "tail waste", "max waste", "min align")
 	prevSize := 0
+	var minAligns [32]int
 	for i, c := range classes {
 		if i == 0 {
 			continue
@@ -252,8 +254,28 @@ func printComment(w io.Writer, classes []class) {
 		objects := spanSize / c.size
 		tailWaste := spanSize - c.size*(spanSize/c.size)
 		maxWaste := float64((c.size-prevSize-1)*objects+tailWaste) / float64(spanSize)
+		alignBits := bits.TrailingZeros(uint(c.size))
+		for i := range minAligns {
+			if i > alignBits {
+				minAligns[i] = 0
+			} else if minAligns[i] == 0 {
+				minAligns[i] = c.size
+			}
+		}
 		prevSize = c.size
-		fmt.Fprintf(w, "// %5d  %9d  %10d  %7d  %10d  %8.2f%%\n", i, c.size, spanSize, objects, tailWaste, 100*maxWaste)
+		fmt.Fprintf(w, "// %5d  %9d  %10d  %7d  %10d  %8.2f%%  %9d\n", i, c.size, spanSize, objects, tailWaste, 100*maxWaste, 1<<alignBits)
+	}
+	fmt.Fprintf(w, "\n")
+
+	fmt.Fprintf(w, "// %-9s  %-4s  %-12s\n", "alignment", "bits", "min obj size")
+	for bits, size := range minAligns {
+		if size == 0 {
+			break
+		}
+		if bits+1 < len(minAligns) && size == minAligns[bits+1] {
+			continue
+		}
+		fmt.Fprintf(w, "// %9d  %4d  %12d\n", 1<<bits, bits, size)
 	}
 	fmt.Fprintf(w, "\n")
 }
diff --git a/src/runtime/sizeclasses.go b/src/runtime/sizeclasses.go
index c5521ce1bd..d71ceeab7b 100644
--- a/src/runtime/sizeclasses.go
+++ b/src/runtime/sizeclasses.go
@@ -3,74 +3,83 @@
 
 package runtime
 
-// class  bytes/obj  bytes/span  objects  tail waste  max waste
-//     1          8        8192     1024           0     87.50%
-//     2         16        8192      512           0     43.75%
-//     3         24        8192      341           8     29.24%
-//     4         32        8192      256           0     21.88%
-//     5         48        8192      170          32     31.52%
-//     6         64        8192      128           0     23.44%
-//     7         80        8192      102          32     19.07%
-//     8         96        8192       85          32     15.95%
-//     9        112        8192       73          16     13.56%
-//    10        128        8192       64           0     11.72%
-//    11        144        8192       56         128     11.82%
-//    12        160        8192       51          32      9.73%
-//    13        176        8192       46          96      9.59%
-//    14        192        8192       42         128      9.25%
-//    15        208        8192       39          80      8.12%
-//    16        224        8192       36         128      8.15%
-//    17        240        8192       34          32      6.62%
-//    18        256        8192       32           0      5.86%
-//    19        288        8192       28         128     12.16%
-//    20        320        8192       25         192     11.80%
-//    21        352        8192       23          96      9.88%
-//    22        384        8192       21         128      9.51%
-//    23        416        8192       19         288     10.71%
-//    24        448        8192       18         128      8.37%
-//    25        480        8192       17          32      6.82%
-//    26        512        8192       16           0      6.05%
-//    27        576        8192       14         128     12.33%
-//    28        640        8192       12         512     15.48%
-//    29        704        8192       11         448     13.93%
-//    30        768        8192       10         512     13.94%
-//    31        896        8192        9         128     15.52%
-//    32       1024        8192        8           0     12.40%
-//    33       1152        8192        7         128     12.41%
-//    34       1280        8192        6         512     15.55%
-//    35       1408       16384       11         896     14.00%
-//    36       1536        8192        5         512     14.00%
-//    37       1792       16384        9         256     15.57%
-//    38       2048        8192        4           0     12.45%
-//    39       2304       16384        7         256     12.46%
-//    40       2688        8192        3         128     15.59%
-//    41       3072       24576        8           0     12.47%
-//    42       3200       16384        5         384      6.22%
-//    43       3456       24576        7         384      8.83%
-//    44       4096        8192        2           0     15.60%
-//    45       4864       24576        5         256     16.65%
-//    46       5376       16384        3         256     10.92%
-//    47       6144       24576        4           0     12.48%
-//    48       6528       32768        5         128      6.23%
-//    49       6784       40960        6         256      4.36%
-//    50       6912       49152        7         768      3.37%
-//    51       8192        8192        1           0     15.61%
-//    52       9472       57344        6         512     14.28%
-//    53       9728       49152        5         512      3.64%
-//    54      10240       40960        4           0      4.99%
-//    55      10880       32768        3         128      6.24%
-//    56      12288       24576        2           0     11.45%
-//    57      13568       40960        3         256      9.99%
-//    58      14336       57344        4           0      5.35%
-//    59      16384       16384        1           0     12.49%
-//    60      18432       73728        4           0     11.11%
-//    61      19072       57344        3         128      3.57%
-//    62      20480       40960        2           0      6.87%
-//    63      21760       65536        3         256      6.25%
-//    64      24576       24576        1           0     11.45%
-//    65      27264       81920        3         128     10.00%
-//    66      28672       57344        2           0      4.91%
-//    67      32768       32768        1           0     12.50%
+// class  bytes/obj  bytes/span  objects  tail waste  max waste  min align
+//     1          8        8192     1024           0     87.50%          8
+//     2         16        8192      512           0     43.75%         16
+//     3         24        8192      341           8     29.24%          8
+//     4         32        8192      256           0     21.88%         32
+//     5         48        8192      170          32     31.52%         16
+//     6         64        8192      128           0     23.44%         64
+//     7         80        8192      102          32     19.07%         16
+//     8         96        8192       85          32     15.95%         32
+//     9        112        8192       73          16     13.56%         16
+//    10        128        8192       64           0     11.72%        128
+//    11        144        8192       56         128     11.82%         16
+//    12        160        8192       51          32      9.73%         32
+//    13        176        8192       46          96      9.59%         16
+//    14        192        8192       42         128      9.25%         64
+//    15        208        8192       39          80      8.12%         16
+//    16        224        8192       36         128      8.15%         32
+//    17        240        8192       34          32      6.62%         16
+//    18        256        8192       32           0      5.86%        256
+//    19        288        8192       28         128     12.16%         32
+//    20        320        8192       25         192     11.80%         64
+//    21        352        8192       23          96      9.88%         32
+//    22        384        8192       21         128      9.51%        128
+//    23        416        8192       19         288     10.71%         32
+//    24        448        8192       18         128      8.37%         64
+//    25        480        8192       17          32      6.82%         32
+//    26        512        8192       16           0      6.05%        512
+//    27        576        8192       14         128     12.33%         64
+//    28        640        8192       12         512     15.48%        128
+//    29        704        8192       11         448     13.93%         64
+//    30        768        8192       10         512     13.94%        256
+//    31        896        8192        9         128     15.52%        128
+//    32       1024        8192        8           0     12.40%       1024
+//    33       1152        8192        7         128     12.41%        128
+//    34       1280        8192        6         512     15.55%        256
+//    35       1408       16384       11         896     14.00%        128
+//    36       1536        8192        5         512     14.00%        512
+//    37       1792       16384        9         256     15.57%        256
+//    38       2048        8192        4           0     12.45%       2048
+//    39       2304       16384        7         256     12.46%        256
+//    40       2688        8192        3         128     15.59%        128
+//    41       3072       24576        8           0     12.47%       1024
+//    42       3200       16384        5         384      6.22%        128
+//    43       3456       24576        7         384      8.83%        128
+//    44       4096        8192        2           0     15.60%       4096
+//    45       4864       24576        5         256     16.65%        256
+//    46       5376       16384        3         256     10.92%        256
+//    47       6144       24576        4           0     12.48%       2048
+//    48       6528       32768        5         128      6.23%        128
+//    49       6784       40960        6         256      4.36%        128
+//    50       6912       49152        7         768      3.37%        256
+//    51       8192        8192        1           0     15.61%       8192
+//    52       9472       57344        6         512     14.28%        256
+//    53       9728       49152        5         512      3.64%        512
+//    54      10240       40960        4           0      4.99%       2048
+//    55      10880       32768        3         128      6.24%        128
+//    56      12288       24576        2           0     11.45%       4096
+//    57      13568       40960        3         256      9.99%        256
+//    58      14336       57344        4           0      5.35%       2048
+//    59      16384       16384        1           0     12.49%      16384
+//    60      18432       73728        4           0     11.11%       2048
+//    61      19072       57344        3         128      3.57%        128
+//    62      20480       40960        2           0      6.87%       4096
+//    63      21760       65536        3         256      6.25%        256
+//    64      24576       24576        1           0     11.45%       8192
+//    65      27264       81920        3         128     10.00%        128
+//    66      28672       57344        2           0      4.91%       4096
+//    67      32768       32768        1           0     12.50%      32768
+
+// alignment  bits  min obj size
+//         8     3             8
+//        16     4            32
+//        32     5           256
+//        64     6           512
+//       128     7           768
+//      4096    12         28672
+//     32768    15         32768
 
 const (
 	_MaxSmallSize   = 32768