t.Errorf("bad pageCache bits: got %016x, want %016x", got.Base(), want.Base())
	}
	if got.Scav() != want.Scav() {
		t.Errorf("bad pageCache scav: got %016x, want %016x", got.Scav(), want.Scav())
	}
}

func TestPageCacheAlloc(t *testing.T) {
	base := PageBase(BaseChunkIdx, 0)
	type hit struct {
		npages uintptr
		base   uintptr
		scav   uintptr
	}
	tests := map[string]struct {
		cache PageCache
		hits  []hit
	}{

		t.Run(name, func(t *testing.T) {
			b := NewPageAlloc(v.before, v.scav)
			defer FreePageAlloc(b)

			for iter, i := range v.hits {
				a, s := b.Alloc(i.npages)
				if a != i.base {
					t.Fatalf("bad alloc #%d: want base 0x%x, got 0x%x", iter+1, i.base, a)
				}
				if s != i.scav {
					t.Fatalf("bad alloc #%d: want scav %d, got %d", iter+1, i.scav, s)
				}
			}
			want := NewPageAlloc(v.after, v.scav)

	if c.cache == 0 {
		return 0, 0
	}
	if npages == 1 {
		i := uintptr(sys.TrailingZeros64(c.cache))
		scav := (c.scav >> i) & 1
		c.cache &^= 1 << i // set bit to mark in-use
		c.scav &^= 1 << i  // clear bit to mark unscavenged
		return c.base + i*pageSize, uintptr(scav) * pageSize
	}
	return c.allocN(npages)
}

// allocN is a helper which attempts to allocate npages worth of pages

		p.scav.index.alloc(sc, pallocChunkPages-si)
		for c := sc + 1; c < ec; c++ {
			chunk := p.chunkOf(c)
			scav += chunk.scavenged.popcntRange(0, pallocChunkPages)
			chunk.allocAll()
			p.scav.index.alloc(c, pallocChunkPages)
		}
		chunk = p.chunkOf(ec)
		scav += chunk.scavenged.popcntRange(0, ei+1)
		chunk.allocRange(0, ei+1)
		p.scav.index.alloc(ec, ei+1)
	}

func NewPageCache(base uintptr, cache, scav uint64) PageCache {
	return PageCache(pageCache{base: base, cache: cache, scav: scav})
}
func (c *PageCache) Empty() bool   { return (*pageCache)(c).empty() }
func (c *PageCache) Base() uintptr { return (*pageCache)(c).base }
func (c *PageCache) Cache() uint64 { return (*pageCache)(c).cache }
func (c *PageCache) Scav() uint64  { return (*pageCache)(c).scav }

	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))

	logPallocChunkPages + 3*summaryLevelBits,
	logPallocChunkPages + 2*summaryLevelBits,
	logPallocChunkPages + 1*summaryLevelBits,
	logPallocChunkPages,
}

// scavengeIndexArray is the backing store for p.scav.index.chunks.
// On 32-bit platforms, it's small enough to just be a global.
var scavengeIndexArray [(1 << heapAddrBits) / pallocChunkBytes]atomicScavChunkData

// See mpagealloc_64bit.go for details.

				lock(&mheap_.lock)

				// Get released stats.
				releasedBg := mheap_.pages.scav.releasedBg.Load()
				releasedEager := mheap_.pages.scav.releasedEager.Load()

				// Print the line.
				printScavTrace(releasedBg, releasedEager, false)

				// Update the stats.
				mheap_.pages.scav.releasedBg.Add(-releasedBg)
				mheap_.pages.scav.releasedEager.Add(-releasedEager)
				unlock(&mheap_.lock)
			})
		}

		sysUsed(unsafe.Pointer(need.base.addr()), need.size(), need.size())
		p.summaryMappedReady += need.size()
	}

	// Update the scavenge index.
	p.summaryMappedReady += p.scav.index.sysGrow(base, limit, p.sysStat)
}

// sysGrow increases the index's backing store in response to a heap growth.
//
// Returns the amount of memory added to sysStat.

		// 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)