diff --git a/libs/ui/BufferHubBuffer.cpp b/libs/ui/BufferHubBuffer.cpp
index 1464e48..5bc113f 100644
--- a/libs/ui/BufferHubBuffer.cpp
+++ b/libs/ui/BufferHubBuffer.cpp
@@ -191,22 +191,22 @@
     mClientStateMask = bufferTraits.client_state_mask();
 
     // TODO(b/112012161) Set up shared fences.
-    ALOGD("BufferHubBuffer::ImportGraphicBuffer: id=%d, buffer_state=%" PRIx64 ".", id(),
+    ALOGD("BufferHubBuffer::ImportGraphicBuffer: id=%d, buffer_state=%" PRIx32 ".", id(),
           buffer_state_->load(std::memory_order_acquire));
     return 0;
 }
 
 int BufferHubBuffer::Gain() {
-    uint64_t current_buffer_state = buffer_state_->load(std::memory_order_acquire);
+    uint32_t current_buffer_state = buffer_state_->load(std::memory_order_acquire);
     if (IsClientGained(current_buffer_state, mClientStateMask)) {
-        ALOGV("%s: Buffer is already gained by this client %" PRIx64 ".", __FUNCTION__,
+        ALOGV("%s: Buffer is already gained by this client %" PRIx32 ".", __FUNCTION__,
               mClientStateMask);
         return 0;
     }
     do {
         if (AnyClientGained(current_buffer_state & (~mClientStateMask)) ||
             AnyClientAcquired(current_buffer_state)) {
-            ALOGE("%s: Buffer is in use, id=%d mClientStateMask=%" PRIx64 " state=%" PRIx64 ".",
+            ALOGE("%s: Buffer is in use, id=%d mClientStateMask=%" PRIx32 " state=%" PRIx32 ".",
                   __FUNCTION__, mId, mClientStateMask, current_buffer_state);
             return -EBUSY;
         }
@@ -220,13 +220,13 @@
 }
 
 int BufferHubBuffer::Post() {
-    uint64_t current_buffer_state = buffer_state_->load(std::memory_order_acquire);
-    uint64_t current_active_clients_bit_mask = 0ULL;
-    uint64_t updated_buffer_state = 0ULL;
+    uint32_t current_buffer_state = buffer_state_->load(std::memory_order_acquire);
+    uint32_t current_active_clients_bit_mask = 0U;
+    uint32_t updated_buffer_state = 0U;
     do {
         if (!IsClientGained(current_buffer_state, mClientStateMask)) {
             ALOGE("%s: Cannot post a buffer that is not gained by this client. buffer_id=%d "
-                  "mClientStateMask=%" PRIx64 " state=%" PRIx64 ".",
+                  "mClientStateMask=%" PRIx32 " state=%" PRIx32 ".",
                   __FUNCTION__, mId, mClientStateMask, current_buffer_state);
             return -EBUSY;
         }
@@ -242,17 +242,17 @@
 }
 
 int BufferHubBuffer::Acquire() {
-    uint64_t current_buffer_state = buffer_state_->load(std::memory_order_acquire);
+    uint32_t current_buffer_state = buffer_state_->load(std::memory_order_acquire);
     if (IsClientAcquired(current_buffer_state, mClientStateMask)) {
-        ALOGV("%s: Buffer is already acquired by this client %" PRIx64 ".", __FUNCTION__,
+        ALOGV("%s: Buffer is already acquired by this client %" PRIx32 ".", __FUNCTION__,
               mClientStateMask);
         return 0;
     }
-    uint64_t updated_buffer_state = 0ULL;
+    uint32_t updated_buffer_state = 0U;
     do {
         if (!IsClientPosted(current_buffer_state, mClientStateMask)) {
             ALOGE("%s: Cannot acquire a buffer that is not in posted state. buffer_id=%d "
-                  "mClientStateMask=%" PRIx64 " state=%" PRIx64 ".",
+                  "mClientStateMask=%" PRIx32 " state=%" PRIx32 ".",
                   __FUNCTION__, mId, mClientStateMask, current_buffer_state);
             return -EBUSY;
         }
@@ -266,13 +266,13 @@
 }
 
 int BufferHubBuffer::Release() {
-    uint64_t current_buffer_state = buffer_state_->load(std::memory_order_acquire);
+    uint32_t current_buffer_state = buffer_state_->load(std::memory_order_acquire);
     if (IsClientReleased(current_buffer_state, mClientStateMask)) {
-        ALOGV("%s: Buffer is already released by this client %" PRIx64 ".", __FUNCTION__,
+        ALOGV("%s: Buffer is already released by this client %" PRIx32 ".", __FUNCTION__,
               mClientStateMask);
         return 0;
     }
-    uint64_t updated_buffer_state = 0ULL;
+    uint32_t updated_buffer_state = 0U;
     do {
         updated_buffer_state = current_buffer_state & (~mClientStateMask);
     } while (!buffer_state_->compare_exchange_weak(current_buffer_state, updated_buffer_state,
diff --git a/libs/ui/include/ui/BufferHubBuffer.h b/libs/ui/include/ui/BufferHubBuffer.h
index 11e9b5c..90dd391 100644
--- a/libs/ui/include/ui/BufferHubBuffer.h
+++ b/libs/ui/include/ui/BufferHubBuffer.h
@@ -86,13 +86,13 @@
     const native_handle_t* DuplicateHandle() { return mBufferHandle.DuplicateHandle(); }
 
     // Returns the current value of MetadataHeader::buffer_state.
-    uint64_t buffer_state() {
+    uint32_t buffer_state() {
         return mMetadata.metadata_header()->buffer_state.load(std::memory_order_acquire);
     }
 
     // A state mask which is unique to a buffer hub client among all its siblings sharing the same
     // concrete graphic buffer.
-    uint64_t client_state_mask() const { return mClientStateMask; }
+    uint32_t client_state_mask() const { return mClientStateMask; }
 
     size_t user_metadata_size() const { return mMetadata.user_metadata_size(); }
 
@@ -154,7 +154,7 @@
 
     // Client state mask of this BufferHubBuffer object. It is unique amoung all
     // clients/users of the buffer.
-    uint64_t mClientStateMask = 0;
+    uint32_t mClientStateMask = 0U;
 
     // Stores ground truth of the buffer.
     AHardwareBuffer_Desc mBufferDesc;
@@ -166,9 +166,9 @@
     // bufferhubd daemon and all buffer clients.
     BufferHubMetadata mMetadata;
     // Shortcuts to the atomics inside the header of mMetadata.
-    std::atomic<uint64_t>* buffer_state_{nullptr};
-    std::atomic<uint64_t>* fence_state_{nullptr};
-    std::atomic<uint64_t>* active_clients_bit_mask_{nullptr};
+    std::atomic<uint32_t>* buffer_state_ = nullptr;
+    std::atomic<uint32_t>* fence_state_ = nullptr;
+    std::atomic<uint32_t>* active_clients_bit_mask_ = nullptr;
 
     // PDX backend.
     BufferHubClient mClient;
diff --git a/libs/ui/include/ui/BufferHubDefs.h b/libs/ui/include/ui/BufferHubDefs.h
index ef6668b..d259fef 100644
--- a/libs/ui/include/ui/BufferHubDefs.h
+++ b/libs/ui/include/ui/BufferHubDefs.h
@@ -29,10 +29,10 @@
 
 namespace BufferHubDefs {
 
-// Single buffer clients (up to 32) ownership signal.
-// 64-bit atomic unsigned int.
-// Each client takes 2 bits. The first bit locates in the first 32 bits of
-// buffer_state; the second bit locates in the last 32 bits of buffer_state.
+// Single buffer clients (up to 16) ownership signal.
+// 32-bit atomic unsigned int.
+// Each client takes 2 bits. The first bit locates in the first 16 bits of
+// buffer_state; the second bit locates in the last 16 bits of buffer_state.
 // Client states:
 // Gained state 11. Exclusive write state.
 // Posted state 10.
@@ -42,88 +42,88 @@
 //  MSB                        LSB
 //   |                          |
 //   v                          v
-// [C31|...|C1|C0|C31| ... |C1|C0]
+// [C15|...|C1|C0|C15| ... |C1|C0]
 
 // Maximum number of clients a buffer can have.
-static constexpr int kMaxNumberOfClients = 32;
+static constexpr int kMaxNumberOfClients = 16;
 
 // Definition of bit masks.
 //  MSB                            LSB
 //   | kHighBitsMask | kLowbitsMask |
 //   v               v              v
-// [b63|   ...   |b32|b31|   ...  |b0]
+// [b31|   ...   |b16|b15|   ...  |b0]
 
-// The location of lower 32 bits in the 64-bit buffer state.
-static constexpr uint64_t kLowbitsMask = (1ULL << kMaxNumberOfClients) - 1ULL;
+// The location of lower 16 bits in the 32-bit buffer state.
+static constexpr uint32_t kLowbitsMask = (1U << kMaxNumberOfClients) - 1U;
 
-// The location of higher 32 bits in the 64-bit buffer state.
-static constexpr uint64_t kHighBitsMask = ~kLowbitsMask;
+// The location of higher 16 bits in the 32-bit buffer state.
+static constexpr uint32_t kHighBitsMask = ~kLowbitsMask;
 
 // The client bit mask of the first client.
-static constexpr uint64_t kFirstClientBitMask = (1ULL << kMaxNumberOfClients) + 1ULL;
+static constexpr uint32_t kFirstClientBitMask = (1U << kMaxNumberOfClients) + 1U;
 
 // Returns true if any of the client is in gained state.
-static inline bool AnyClientGained(uint64_t state) {
-    uint64_t high_bits = state >> kMaxNumberOfClients;
-    uint64_t low_bits = state & kLowbitsMask;
-    return high_bits == low_bits && low_bits != 0ULL;
+static inline bool AnyClientGained(uint32_t state) {
+    uint32_t high_bits = state >> kMaxNumberOfClients;
+    uint32_t low_bits = state & kLowbitsMask;
+    return high_bits == low_bits && low_bits != 0U;
 }
 
 // Returns true if the input client is in gained state.
-static inline bool IsClientGained(uint64_t state, uint64_t client_bit_mask) {
+static inline bool IsClientGained(uint32_t state, uint32_t client_bit_mask) {
     return state == client_bit_mask;
 }
 
 // Returns true if any of the client is in posted state.
-static inline bool AnyClientPosted(uint64_t state) {
-    uint64_t high_bits = state >> kMaxNumberOfClients;
-    uint64_t low_bits = state & kLowbitsMask;
-    uint64_t posted_or_acquired = high_bits ^ low_bits;
+static inline bool AnyClientPosted(uint32_t state) {
+    uint32_t high_bits = state >> kMaxNumberOfClients;
+    uint32_t low_bits = state & kLowbitsMask;
+    uint32_t posted_or_acquired = high_bits ^ low_bits;
     return posted_or_acquired & high_bits;
 }
 
 // Returns true if the input client is in posted state.
-static inline bool IsClientPosted(uint64_t state, uint64_t client_bit_mask) {
-    uint64_t client_bits = state & client_bit_mask;
-    if (client_bits == 0ULL) return false;
-    uint64_t low_bits = client_bits & kLowbitsMask;
-    return low_bits == 0ULL;
+static inline bool IsClientPosted(uint32_t state, uint32_t client_bit_mask) {
+    uint32_t client_bits = state & client_bit_mask;
+    if (client_bits == 0U) return false;
+    uint32_t low_bits = client_bits & kLowbitsMask;
+    return low_bits == 0U;
 }
 
 // Return true if any of the client is in acquired state.
-static inline bool AnyClientAcquired(uint64_t state) {
-    uint64_t high_bits = state >> kMaxNumberOfClients;
-    uint64_t low_bits = state & kLowbitsMask;
-    uint64_t posted_or_acquired = high_bits ^ low_bits;
+static inline bool AnyClientAcquired(uint32_t state) {
+    uint32_t high_bits = state >> kMaxNumberOfClients;
+    uint32_t low_bits = state & kLowbitsMask;
+    uint32_t posted_or_acquired = high_bits ^ low_bits;
     return posted_or_acquired & low_bits;
 }
 
 // Return true if the input client is in acquired state.
-static inline bool IsClientAcquired(uint64_t state, uint64_t client_bit_mask) {
-    uint64_t client_bits = state & client_bit_mask;
-    if (client_bits == 0ULL) return false;
-    uint64_t high_bits = client_bits & kHighBitsMask;
-    return high_bits == 0ULL;
+static inline bool IsClientAcquired(uint32_t state, uint32_t client_bit_mask) {
+    uint32_t client_bits = state & client_bit_mask;
+    if (client_bits == 0U) return false;
+    uint32_t high_bits = client_bits & kHighBitsMask;
+    return high_bits == 0U;
 }
 
 // Returns true if all clients are in released state.
-static inline bool IsBufferReleased(uint64_t state) {
-    return state == 0ULL;
+static inline bool IsBufferReleased(uint32_t state) {
+    return state == 0U;
 }
 
 // Returns true if the input client is in released state.
-static inline bool IsClientReleased(uint64_t state, uint64_t client_bit_mask) {
-    return (state & client_bit_mask) == 0ULL;
+static inline bool IsClientReleased(uint32_t state, uint32_t client_bit_mask) {
+    return (state & client_bit_mask) == 0U;
 }
 
 // Returns the next available buffer client's client_state_masks.
 // @params union_bits. Union of all existing clients' client_state_masks.
-static inline uint64_t FindNextAvailableClientStateMask(uint64_t union_bits) {
-    uint64_t low_union = union_bits & kLowbitsMask;
-    if (low_union == kLowbitsMask) return 0ULL;
-    uint64_t incremented = low_union + 1ULL;
-    uint64_t difference = incremented ^ low_union;
-    uint64_t new_low_bit = (difference + 1ULL) >> 1;
+static inline uint32_t FindNextAvailableClientStateMask(uint32_t union_bits) {
+    uint32_t low_union = union_bits & kLowbitsMask;
+    if (low_union == kLowbitsMask) return 0U;
+    uint32_t incremented = low_union + 1U;
+    uint32_t difference = incremented ^ low_union;
+    uint32_t new_low_bit = (difference + 1U) >> 1;
     return new_low_bit + (new_low_bit << kMaxNumberOfClients);
 }
 
@@ -135,15 +135,18 @@
 
     // Every client takes up one bit from the higher 32 bits and one bit from the lower 32 bits in
     // buffer_state.
-    std::atomic<uint64_t> buffer_state;
+    std::atomic<uint32_t> buffer_state;
 
     // Every client takes up one bit in fence_state. Only the lower 32 bits are valid. The upper 32
     // bits are there for easier manipulation, but the value should be ignored.
-    std::atomic<uint64_t> fence_state;
+    std::atomic<uint32_t> fence_state;
 
     // Every client takes up one bit from the higher 32 bits and one bit from the lower 32 bits in
     // active_clients_bit_mask.
-    std::atomic<uint64_t> active_clients_bit_mask;
+    std::atomic<uint32_t> active_clients_bit_mask;
+
+    // Explicit padding 4 bytes.
+    uint32_t padding;
 
     // The index of the buffer queue where the buffer belongs to.
     uint64_t queue_index;
@@ -152,7 +155,7 @@
     DvrNativeBufferMetadata metadata;
 };
 
-static_assert(sizeof(MetadataHeader) == 136, "Unexpected MetadataHeader size");
+static_assert(sizeof(MetadataHeader) == 128, "Unexpected MetadataHeader size");
 static constexpr size_t kMetadataHeaderSize = sizeof(MetadataHeader);
 
 } // namespace BufferHubDefs
diff --git a/libs/ui/tests/BufferHubBuffer_test.cpp b/libs/ui/tests/BufferHubBuffer_test.cpp
index f616785..a894f20 100644
--- a/libs/ui/tests/BufferHubBuffer_test.cpp
+++ b/libs/ui/tests/BufferHubBuffer_test.cpp
@@ -67,9 +67,9 @@
     }
 
     std::unique_ptr<BufferHubBuffer> b1;
-    uint64_t b1ClientMask = 0ULL;
+    uint64_t b1ClientMask = 0U;
     std::unique_ptr<BufferHubBuffer> b2;
-    uint64_t b2ClientMask = 0ULL;
+    uint64_t b2ClientMask = 0U;
 
 private:
     // Creates b1 and b2 as the clients of the same buffer for testing.
@@ -79,13 +79,13 @@
 void BufferHubBufferStateTransitionTest::CreateTwoClientsOfABuffer() {
     b1 = BufferHubBuffer::Create(kWidth, kHeight, kLayerCount, kFormat, kUsage, kUserMetadataSize);
     b1ClientMask = b1->client_state_mask();
-    ASSERT_NE(b1ClientMask, 0ULL);
+    ASSERT_NE(b1ClientMask, 0U);
     auto statusOrHandle = b1->Duplicate();
     ASSERT_TRUE(statusOrHandle);
     LocalChannelHandle h2 = statusOrHandle.take();
     b2 = BufferHubBuffer::Import(std::move(h2));
     b2ClientMask = b2->client_state_mask();
-    ASSERT_NE(b2ClientMask, 0ULL);
+    ASSERT_NE(b2ClientMask, 0U);
     ASSERT_NE(b2ClientMask, b1ClientMask);
 }
 
@@ -126,7 +126,7 @@
                                       kUserMetadataSize);
     int id1 = b1->id();
     uint64_t bufferStateMask1 = b1->client_state_mask();
-    EXPECT_NE(bufferStateMask1, 0ULL);
+    EXPECT_NE(bufferStateMask1, 0U);
     EXPECT_TRUE(b1->IsValid());
     EXPECT_EQ(b1->user_metadata_size(), kUserMetadataSize);
 
@@ -149,7 +149,7 @@
 
     int id2 = b2->id();
     uint64_t bufferStateMask2 = b2->client_state_mask();
-    EXPECT_NE(bufferStateMask2, 0ULL);
+    EXPECT_NE(bufferStateMask2, 0U);
 
     // These two buffer instances are based on the same physical buffer under the
     // hood, so they should share the same id.