nbytes := npages * pageSize
	if scav != 0 {
		// sysUsed all the pages that are actually available
		// in the span since some of them might be scavenged.
		sysUsed(unsafe.Pointer(base), nbytes, scav)
		gcController.heapReleased.add(-int64(scav))
	}
	// Update stats.
	gcController.heapFree.add(-int64(nbytes - scav))
	if typ == spanAllocHeap {
		gcController.heapInUse.add(int64(nbytes))

		// response, broke down. This may be transient, so temporarily switch to
		// sleeping a fixed, conservative amount.
		s.sleepRatio = startingScavSleepRatio
		s.controllerCooldown = 5e9 // 5 seconds.

		// Signal the scav trace printer to output this.
		s.controllerFailed()
	}
}

// controllerFailed indicates that the scavenger's scheduling
// controller failed.
func (s *scavengerState) controllerFailed() {
	lock(&s.lock)

// improve parallelism, the garbage collector breaks up scan jobs for
// objects larger than maxObletBytes into "oblets" of at most
// maxObletBytes. When scanning encounters the beginning of a large
// object, it scans only the first oblet and enqueues the remaining
// oblets as new scan jobs.

package runtime

import (
	"internal/cpu"
	"internal/runtime/atomic"
	"unsafe"

build-scan-infrastructure.png...

	fixedRootFreeGStacks
	fixedRootCount

	// rootBlockBytes is the number of bytes to scan per data or
	// BSS root.
	rootBlockBytes = 256 << 10

	// maxObletBytes is the maximum bytes of an object to scan at
	// once. Larger objects will be split up into "oblets" of at
	// most this size. Since we can scan 1–2 MB/ms, 128 KB bounds
	// scan preemption at ~100 µs.
	//
	// This must be > _MaxSmallSize so that the object base is the

	// seven lines a few times in this source file. The copies below
	// refer back to the pattern established by this original as the
	// "LMS-substring iterator".
	//
	// In every scan through the text, c0, c1 are successive characters of text.
	// In this backward scan, c0 == text[i] and c1 == text[i+1].
	// By scanning backward, we can keep track of whether the current
	// position is type-S or type-L according to the usual definition:
	//

	// unlike heapLive, heapMarked does not change until the
	// next mark termination.
	heapMarked uint64

	// heapScanWork is the total heap scan work performed this cycle.
	// stackScanWork is the total stack scan work performed this cycle.
	// globalsScanWork is the total globals scan work performed this cycle.
	//
	// These are updated atomically during the cycle. Updates occur in

	// In both cases the algorithm is a linear scan over the two
	// lists - T's methods and V's methods - simultaneously.
	// Since method tables are stored in a unique sorted order
	// (alphabetical, with no duplicate method names), the scan
	// through V's methods must hit a match for each of T's
	// methods along the way, or else V does not implement T.
	// This lets us run the scan in overall linear time instead of

	}
}

type DoubleInt64 struct {
	data int64
}

func (t *DoubleInt64) Scan(val interface{}) error {
	switch v := val.(type) {
	case int64:
		t.data = v * 2
		return nil
	default:
		return fmt.Errorf("DoubleInt64 cant not scan with:%v", v)
	}
}

// https://github.com/go-gorm/gorm/issues/5091
func TestQueryScannerWithSingleColumn(t *testing.T) {

	// contain defers (d3 in this case) for dead frames. The inversion here
	// always indicates a dead frame, and the effect of the inversion on the
	// scan is to hide those dead frames, so the scan is still okay:
	// what's left on the panic stack are exactly (and only) the dead frames.
	//
	// We require callback != nil here because only when callback != nil