runtime: integrate new page allocator into runtime

This change integrates all the bits and pieces of the new page allocator
into the runtime, behind a global constant.

Updates #35112.

Change-Id: I6696bde7bab098a498ab37ed2a2caad2a05d30ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/201764
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/malloc_test.go

@@ -176,6 +176,23 @@ func TestPhysicalMemoryUtilization(t *testing.T) {
 	}
 }
 
+func TestScavengedBitsCleared(t *testing.T) {
+	if OldPageAllocator {
+		// This test is only relevant for the new page allocator.
+		return
+	}
+	var mismatches [128]BitsMismatch
+	if n, ok := CheckScavengedBitsCleared(mismatches[:]); !ok {
+		t.Errorf("uncleared scavenged bits")
+		for _, m := range mismatches[:n] {
+			t.Logf("\t@ address 0x%x", m.Base)
+			t.Logf("\t|  got: %064b", m.Got)
+			t.Logf("\t| want: %064b", m.Want)
+		}
+		t.FailNow()
+	}
+}
+
 type acLink struct {
 	x [1 << 20]byte
 }