diff --git a/syncmap/map.go b/syncmap/map.go
index 1efbcb2..80e1584 100644
--- a/syncmap/map.go
+++ b/syncmap/map.go
@@ -11,9 +11,10 @@
 import (
 	"sync"
 	"sync/atomic"
+	"unsafe"
 )
 
-// Map is a concurrent map with amortized-constant-time operations.
+// Map is a concurrent map with amortized-constant-time loads, stores, and deletes.
 // It is safe for multiple goroutines to call a Map's methods concurrently.
 //
 // The zero Map is valid and empty.
@@ -22,145 +23,313 @@
 type Map struct {
 	mu sync.Mutex
 
-	// clean is a copy of the map's contents that will never be overwritten, and
-	// is thus safe for concurrent lookups without additional synchronization.
+	// read contains the portion of the map's contents that are safe for
+	// concurrent access (with or without mu held).
 	//
-	// A nil clean map indicates that the current map contents are stored in the
-	// dirty field instead.
-	// If clean is non-nil, its contents are up-to-date.
+	// The read field itself is always safe to load, but must only be stored with
+	// mu held.
 	//
-	// clean is always safe to load, but must only be stored with mu held.
-	clean atomic.Value // map[interface{}]interface{}
+	// Entries stored in read may be updated concurrently without mu, but updating
+	// a previously-expunged entry requires that the entry be copied to the dirty
+	// map and unexpunged with mu held.
+	read atomic.Value // readOnly
 
-	// dirty is a copy of the map to which all writes occur.
+	// dirty contains the portion of the map's contents that require mu to be
+	// held. To ensure that the dirty map can be promoted to the read map quickly,
+	// it also includes all of the non-expunged entries in the read map.
 	//
-	// A nil dirty map indicates that the current map contents are either empty or
-	// stored in the clean field.
+	// Expunged entries are not stored in the dirty map. An expunged entry in the
+	// clean map must be unexpunged and added to the dirty map before a new value
+	// can be stored to it.
 	//
 	// If the dirty map is nil, the next write to the map will initialize it by
-	// making a deep copy of the clean map, then setting the clean map to nil.
-	dirty map[interface{}]interface{}
+	// making a shallow copy of the clean map, omitting stale entries.
+	dirty map[interface{}]*entry
 
-	// misses counts the number of Load calls for which the clean map was nil
-	// since the last write.
+	// misses counts the number of loads since the read map was last updated that
+	// needed to lock mu to determine whether the key was present.
 	//
-	// Once enough Load misses have occurred to cover the cost of a copy, the
-	// dirty map will be promoted to clean and any subsequent writes will make
-	// a new copy.
+	// Once enough misses have occurred to cover the cost of copying the dirty
+	// map, the dirty map will be promoted to the read map (in the unamended
+	// state) and the next store to the map will make a new dirty copy.
 	misses int
 }
 
+// readOnly is an immutable struct stored atomically in the Map.read field.
+type readOnly struct {
+	m       map[interface{}]*entry
+	amended bool // true if the dirty map contains some key not in m.
+}
+
+// expunged is an arbitrary pointer that marks entries which have been deleted
+// from the dirty map.
+var expunged = unsafe.Pointer(new(interface{}))
+
+// An entry is a slot in the map corresponding to a particular key.
+type entry struct {
+	// p points to the interface{} value stored for the entry.
+	//
+	// If p == nil, the entry has been deleted and m.dirty == nil.
+	//
+	// If p == expunged, the entry has been deleted, m.dirty != nil, and the entry
+	// is missing from m.dirty.
+	//
+	// Otherwise, the entry is valid and recorded in m.read.m[key] and, if m.dirty
+	// != nil, in m.dirty[key].
+	//
+	// An entry can be deleted by atomic replacement with nil: when m.dirty is
+	// next created, it will atomically replace nil with expunged and leave
+	// m.dirty[key] unset.
+	//
+	// An entry's associated value can be updated by atomic replacement, provided
+	// p != expunged. If p == expunged, an entry's associated value can be updated
+	// only after first setting m.dirty[key] = e so that lookups using the dirty
+	// map find the entry.
+	p unsafe.Pointer // *interface{}
+}
+
+func newEntry(i interface{}) *entry {
+	return &entry{p: unsafe.Pointer(&i)}
+}
+
 // Load returns the value stored in the map for a key, or nil if no
 // value is present.
 // The ok result indicates whether value was found in the map.
 func (m *Map) Load(key interface{}) (value interface{}, ok bool) {
-	clean, _ := m.clean.Load().(map[interface{}]interface{})
-	if clean != nil {
-		value, ok = clean[key]
-		return value, ok
-	}
-
-	m.mu.Lock()
-	if m.dirty == nil {
-		clean, _ := m.clean.Load().(map[interface{}]interface{})
-		if clean == nil {
-			// Completely empty — promote to clean immediately.
-			m.clean.Store(map[interface{}]interface{}{})
-		} else {
-			value, ok = clean[key]
+	read, _ := m.read.Load().(readOnly)
+	e, ok := read.m[key]
+	if !ok && read.amended {
+		m.mu.Lock()
+		// Avoid reporting a spurious miss if m.dirty got promoted while we were
+		// blocked on m.mu. (If further loads of the same key will not miss, it's
+		// not worth copying the dirty map for this key.)
+		read, _ = m.read.Load().(readOnly)
+		e, ok = read.m[key]
+		if !ok && read.amended {
+			e, ok = m.dirty[key]
+			// Regardless of whether the entry was present, record a miss: this key
+			// will take the slow path until the dirty map is promoted to the read
+			// map.
+			m.missLocked()
 		}
 		m.mu.Unlock()
-		return value, ok
 	}
-	value, ok = m.dirty[key]
-	m.missLocked()
-	m.mu.Unlock()
-	return value, ok
+	if !ok {
+		return nil, false
+	}
+	return e.load()
+}
+
+func (e *entry) load() (value interface{}, ok bool) {
+	p := atomic.LoadPointer(&e.p)
+	if p == nil || p == expunged {
+		return nil, false
+	}
+	return *(*interface{})(p), true
 }
 
 // Store sets the value for a key.
 func (m *Map) Store(key, value interface{}) {
+	read, _ := m.read.Load().(readOnly)
+	if e, ok := read.m[key]; ok && e.tryStore(&value) {
+		return
+	}
+
 	m.mu.Lock()
-	m.dirtyLocked()
-	m.dirty[key] = value
+	read, _ = m.read.Load().(readOnly)
+	if e, ok := read.m[key]; ok {
+		if e.unexpungeLocked() {
+			// The entry was previously expunged, which implies that there is a
+			// non-nil dirty map and this entry is not in it.
+			m.dirty[key] = e
+		}
+		e.storeLocked(&value)
+	} else if e, ok := m.dirty[key]; ok {
+		e.storeLocked(&value)
+	} else {
+		if !read.amended {
+			// We're adding the first new key to the dirty map.
+			// Make sure it is allocated and mark the read-only map as incomplete.
+			m.dirtyLocked()
+			m.read.Store(readOnly{m: read.m, amended: true})
+		}
+		m.dirty[key] = newEntry(value)
+	}
 	m.mu.Unlock()
 }
 
+// tryStore stores a value if the entry has not been expunged.
+//
+// If the entry is expunged, tryStore returns false and leaves the entry
+// unchanged.
+func (e *entry) tryStore(i *interface{}) bool {
+	p := atomic.LoadPointer(&e.p)
+	if p == expunged {
+		return false
+	}
+	for {
+		if atomic.CompareAndSwapPointer(&e.p, p, unsafe.Pointer(i)) {
+			return true
+		}
+		p = atomic.LoadPointer(&e.p)
+		if p == expunged {
+			return false
+		}
+	}
+}
+
+// unexpungeLocked ensures that the entry is not marked as expunged.
+//
+// If the entry was previously expunged, it must be added to the dirty map
+// before m.mu is unlocked.
+func (e *entry) unexpungeLocked() (wasExpunged bool) {
+	return atomic.CompareAndSwapPointer(&e.p, expunged, nil)
+}
+
+// storeLocked unconditionally stores a value to the entry.
+//
+// The entry must be known not to be expunged.
+func (e *entry) storeLocked(i *interface{}) {
+	atomic.StorePointer(&e.p, unsafe.Pointer(i))
+}
+
 // LoadOrStore returns the existing value for the key if present.
 // Otherwise, it stores and returns the given value.
 // The loaded result is true if the value was loaded, false if stored.
 func (m *Map) LoadOrStore(key, value interface{}) (actual interface{}, loaded bool) {
 	// Avoid locking if it's a clean hit.
-	clean, _ := m.clean.Load().(map[interface{}]interface{})
-	actual, loaded = clean[key]
-	if loaded {
-		return actual, true
+	read, _ := m.read.Load().(readOnly)
+	if e, ok := read.m[key]; ok {
+		actual, loaded, ok := e.tryLoadOrStore(value)
+		if ok {
+			return actual, loaded
+		}
 	}
 
 	m.mu.Lock()
-	if m.dirty == nil {
-		// Reload clean in case it changed while we were waiting on m.mu.
-		clean, _ := m.clean.Load().(map[interface{}]interface{})
-		actual, loaded = clean[key]
-		if loaded {
-			m.mu.Unlock()
-			return actual, true
+	read, _ = m.read.Load().(readOnly)
+	if e, ok := read.m[key]; ok {
+		if e.unexpungeLocked() {
+			m.dirty[key] = e
 		}
+		actual, loaded, _ = e.tryLoadOrStore(value)
+	} else if e, ok := m.dirty[key]; ok {
+		actual, loaded, _ = e.tryLoadOrStore(value)
+		m.missLocked()
 	} else {
-		actual, loaded = m.dirty[key]
-		if loaded {
-			m.missLocked()
-			m.mu.Unlock()
-			return actual, true
+		if !read.amended {
+			// We're adding the first new key to the dirty map.
+			// Make sure it is allocated and mark the read-only map as incomplete.
+			m.dirtyLocked()
+			m.read.Store(readOnly{m: read.m, amended: true})
 		}
+		m.dirty[key] = newEntry(value)
+		actual, loaded = value, false
+	}
+	m.mu.Unlock()
+
+	return actual, loaded
+}
+
+// tryLoadOrStore atomically loads or stores a value if the entry is not
+// expunged.
+//
+// If the entry is expunged, tryLoadOrStore leaves the entry unchanged and
+// returns with ok==false.
+func (e *entry) tryLoadOrStore(i interface{}) (actual interface{}, loaded, ok bool) {
+	p := atomic.LoadPointer(&e.p)
+	if p == expunged {
+		return nil, false, false
+	}
+	if p != nil {
+		return *(*interface{})(p), true, true
 	}
 
-	m.dirtyLocked()
-	m.dirty[key] = value
-	actual = value
-	m.mu.Unlock()
-	return actual, false
+	// Copy the interface after the first load to make this method more amenable
+	// to escape analysis: if we hit the "load" path or the entry is expunged, we
+	// shouldn't bother heap-allocating.
+	ic := i
+	for {
+		if atomic.CompareAndSwapPointer(&e.p, nil, unsafe.Pointer(&ic)) {
+			return i, false, true
+		}
+		p = atomic.LoadPointer(&e.p)
+		if p == expunged {
+			return nil, false, false
+		}
+		if p != nil {
+			return *(*interface{})(p), true, true
+		}
+	}
 }
 
 // Delete deletes the value for a key.
 func (m *Map) Delete(key interface{}) {
-	m.mu.Lock()
-	m.dirtyLocked()
-	delete(m.dirty, key)
-	m.mu.Unlock()
+	read, _ := m.read.Load().(readOnly)
+	e, ok := read.m[key]
+	if !ok && read.amended {
+		m.mu.Lock()
+		read, _ = m.read.Load().(readOnly)
+		e, ok = read.m[key]
+		if !ok && read.amended {
+			delete(m.dirty, key)
+		}
+		m.mu.Unlock()
+	}
+	if ok {
+		e.delete()
+	}
+}
+
+func (e *entry) delete() (hadValue bool) {
+	for {
+		p := atomic.LoadPointer(&e.p)
+		if p == nil || p == expunged {
+			return false
+		}
+		if atomic.CompareAndSwapPointer(&e.p, p, nil) {
+			return true
+		}
+	}
 }
 
 // Range calls f sequentially for each key and value present in the map.
 // If f returns false, range stops the iteration.
 //
-// Calls to other Map methods may block until Range returns.
-// The function f must not call any other methods on the Map.
-//
 // Range does not necessarily correspond to any consistent snapshot of the Map's
 // contents: no key will be visited more than once, but if the value for any key
 // is stored or deleted concurrently, Range may reflect any mapping for that key
 // from any point during the Range call.
+//
+// Range may be O(N) with the number of elements in the map even if f returns
+// false after a constant number of calls.
 func (m *Map) Range(f func(key, value interface{}) bool) {
-	clean, _ := m.clean.Load().(map[interface{}]interface{})
-	if clean == nil {
+	// We need to be able to iterate over all of the keys that were already
+	// present at the start of the call to Range.
+	// If read.amended is false, then read.m satisfies that property without
+	// requiring us to hold m.mu for a long time.
+	read, _ := m.read.Load().(readOnly)
+	if read.amended {
+		// m.dirty contains keys not in read.m. Fortunately, Range is already O(N)
+		// (assuming the caller does not break out early), so a call to Range
+		// amortizes an entire copy of the map: we can promote the dirty copy
+		// immediately!
 		m.mu.Lock()
-		if m.dirty == nil {
-			clean, _ = m.clean.Load().(map[interface{}]interface{})
-			if clean == nil {
-				// Completely empty — add an empty map to bypass m.mu next time.
-				m.clean.Store(map[interface{}]interface{}{})
-			}
-		} else {
-			// Range is already O(N), so a call to Range amortizes an entire copy of
-			// the map.  If it is dirty, we can promote it to clean immediately!
-			clean = m.dirty
-			m.clean.Store(clean)
+		read, _ = m.read.Load().(readOnly)
+		if read.amended {
+			read = readOnly{m: m.dirty}
+			m.read.Store(read)
 			m.dirty = nil
+			m.misses = 0
 		}
 		m.mu.Unlock()
 	}
 
-	for k, v := range clean {
+	for k, e := range read.m {
+		v, ok := e.load()
+		if !ok {
+			continue
+		}
 		if !f(k, v) {
 			break
 		}
@@ -168,25 +337,36 @@
 }
 
 func (m *Map) missLocked() {
-	if m.misses++; m.misses >= len(m.dirty) {
-		m.clean.Store(m.dirty)
-		m.dirty = nil
+	m.misses++
+	if m.misses < len(m.dirty) {
+		return
 	}
+	m.read.Store(readOnly{m: m.dirty})
+	m.dirty = nil
+	m.misses = 0
 }
 
-// dirtyLocked prepares the map for a subsequent write.
-// It ensures that the dirty field is non-nil and clean is nil by making a deep
-// copy of clean.
 func (m *Map) dirtyLocked() {
-	m.misses = 0
 	if m.dirty != nil {
 		return
 	}
 
-	clean, _ := m.clean.Load().(map[interface{}]interface{})
-	m.dirty = make(map[interface{}]interface{}, len(clean))
-	for k, v := range clean {
-		m.dirty[k] = v
+	read, _ := m.read.Load().(readOnly)
+	m.dirty = make(map[interface{}]*entry, len(read.m))
+	for k, e := range read.m {
+		if !e.tryExpungeLocked() {
+			m.dirty[k] = e
+		}
 	}
-	m.clean.Store(map[interface{}]interface{}(nil))
+}
+
+func (e *entry) tryExpungeLocked() (isExpunged bool) {
+	p := atomic.LoadPointer(&e.p)
+	for p == nil {
+		if atomic.CompareAndSwapPointer(&e.p, nil, expunged) {
+			return true
+		}
+		p = atomic.LoadPointer(&e.p)
+	}
+	return p == expunged
 }