Memory use reduction: smaller/single MMStorage

PiperOrigin-RevId: 804865029

gemma/activations.h

@@ -179,7 +179,7 @@ struct Activations {
 
   MatStorageT<float> x;  // input
   MatStorageT<BF16> x_bf;  // output of final RMSNorm, input to EmbeddingMatmul
-  MatStorageT<float> logits;
+  MatStorageT<float> logits;      // TODO: BF16 after Softmax supports that.
   MatStorageT<uint32_t> sampled;  // batch_size x 3 (padded)
 
   // Gated FFW

gemma/gemma.h

@@ -127,7 +127,7 @@ class QBatch {
         max_size_(max_size),
         queries_(queries),
         size_(HWY_MIN(max_size_, queries_.NumQueries() - start_)) {
-    HWY_ASSERT(max_size_ <= 4096);  // non_eos uses `BitSet4096`.
+    HWY_ASSERT(max_size_ <= kMaxBatchSize);
     HWY_DASSERT(size_ != 0);
     HWY_DASSERT(start_ + size_ <= queries_.NumQueries());
   }

ops/matmul-inl.h

@@ -797,9 +797,10 @@ class MMImpl {
       return View(A, 0, 0, A.Cols());
     } else {
       // Always decompress. To reduce code size/compile time, we no longer
-      // support a separate F32 kernel; most A are already BF16.
+      // support a separate F32 kernel; most A are already BF16. We also only
-      const StridedViewBF A_view =
+      // have a single MMStorage.
-          args.env->storage[args.options.cluster_idx].A(A.Extents());
+      HWY_ASSERT(args.options.cluster_idx == 0);
+      const StridedViewBF A_view = args.env->storage.A(A.Extents());
       DecompressA(A, A_view, args);
       return A_view;
     }

ops/matmul.cc

@@ -346,14 +346,10 @@ std::vector<MMConfig> MMCandidates(const CacheInfo& cache, size_t M, size_t K,
   return GenerateCandidates(cache, M, K, N, sizeof_TC, print_config)();
 }
 
-MatMulEnv::MatMulEnv(ThreadingContext& ctx) : ctx(ctx) {
+MatMulEnv::MatMulEnv(ThreadingContext& ctx) : ctx(ctx), storage(ctx.allocator) {
-  // Create storage per cluster. This only applies to in-cluster parallelism.
-  // For nested and sequential parallelism, a single MMStorage is used.
   const size_t num_clusters = ctx.pools.AllClusters(/*pkg_idx=*/0).NumWorkers();
   per_cluster.resize(num_clusters);
-  storage.reserve(num_clusters);
   for (size_t cluster_idx = 0; cluster_idx < num_clusters; ++cluster_idx) {
-    storage.push_back(MMStorage(ctx.allocator));
     row_ptrs.push_back(hwy::AllocateAligned<uint8_t*>(kMaxBatchSize));  // C
   }
 

ops/matmul.h

@@ -306,11 +306,11 @@ using StridedViewD = StridedView<double>;
 class MMStorage {
  public:
   // Compile-time bounds on matrix columns to enable pre-allocating storage
-  // and reusing it across `MatMul` calls.
+  // and reusing it across `MatMul` calls. Sufficient for Gemma 2 27B.
-  static constexpr size_t kMaxK = 64 * 1024;
+  static constexpr size_t kMaxK = 36 * 1024;
 
   MMStorage(const Allocator& allocator)
-      // 0.5 GiB. Must be padded, see `DoDecompressA`.
+      // 288 MiB. Must be padded, see `DoDecompressA`.
       : A_("A_bf", Extents2D(kMaxBatchSize, kMaxK), allocator,
            MatPadding::kOdd) {}
 
@@ -673,7 +673,7 @@ struct MatMulEnv {
   // Whether to print the best config immediately after autotuning finished.
   bool print_best = false;
 
-  std::vector<MMStorage> storage;
+  MMStorage storage;
 
   struct PerCluster {
     MMKeys keys;

ops/ops-inl.h

@@ -614,6 +614,7 @@ HWY_NOINLINE HWY_MAYBE_UNUSED void MulByConstAndAdd(
 }
 
 // See below for a specialized version for top-1 sampling.
+// TODO: support bf16 logits using Decompress2.
 static HWY_NOINLINE void Softmax(Logits logits, hwy::Profiler& p,
                                  const size_t worker,
                                  float temperature = 1.0f) {

util/basics.h

@@ -30,7 +30,7 @@
 
 namespace gcpp {
 
-// TODO: extend to 16k after updating non_eos.
+// For hwy::BitSet4096. Note that KVs are extremely large for such batches.
 HWY_INLINE_VAR constexpr size_t kMaxBatchSize = 4096;
 
 enum class Tristate : int32_t { kFalse = 0, kTrue = 1, kDefault = -1 };