bugfix: fix wrong padded_batch_size_ (#296)

In #294 , we set `padded_batch_size_` to `num_kv_heads * batch_size`,
which should be `batch_size`

include/flashinfer/attention/handler.cuh

@@ -318,56 +318,56 @@ class BatchDecodeHandler {
                 << " initialized for CUDAGraph";
         throw std::runtime_error(err_msg.str());
       }
-      size_t padded_batch_size_after_partition = max_grid_size / num_kv_heads;
+      size_t padded_batch_size = max_grid_size / num_kv_heads;
       if (tmp_size > 0) {
-        padded_batch_size_ = padded_batch_size_after_partition;
+        padded_batch_size_ = padded_batch_size;
         AlignedAllocator allocator(buffer, workspace_size_in_bytes);
         tmp_v_ = allocator.aligned_alloc<void>(
-            num_qo_heads * padded_batch_size_after_partition * HEAD_DIM * sizeof(DTypeOut), 16);
+            num_qo_heads * padded_batch_size * HEAD_DIM * sizeof(DTypeOut), 16);
         tmp_s_ = allocator.aligned_alloc<void>(
-            num_qo_heads * padded_batch_size_after_partition * 2 * sizeof(float), 16);
+            num_qo_heads * padded_batch_size * 2 * sizeof(float), 16);
         new_indptr_ = allocator.aligned_alloc<void>(
-            (padded_batch_size_after_partition + 1) * sizeof(IdType), 16);
+            (padded_batch_size + 1) * sizeof(IdType), 16);
 
         void* new_indptr_h_ = page_locked_buffer_;
         new_last_page_len_ =
-            allocator.aligned_alloc<void>(padded_batch_size_after_partition * sizeof(IdType), 16);
+            allocator.aligned_alloc<void>(padded_batch_size * sizeof(IdType), 16);
         void* new_last_page_len_h_ =
             (char*)page_locked_buffer_ + ((char*)new_last_page_len_ - (char*)new_indptr_);
         chunk_indptr_ = allocator.aligned_alloc<void>(
-            (padded_batch_size_after_partition + 1) * sizeof(IdType), 16);
+            (padded_batch_size + 1) * sizeof(IdType), 16);
         void* chunk_indptr_h_ =
             (char*)page_locked_buffer_ + ((char*)chunk_indptr_ - (char*)new_indptr_);
         batch_idx_map_ =
-            allocator.aligned_alloc<void>(padded_batch_size_after_partition * sizeof(IdType), 16);
+            allocator.aligned_alloc<void>(padded_batch_size * sizeof(IdType), 16);
         void* batch_idx_map_h_ =
             (char*)page_locked_buffer_ + ((char*)batch_idx_map_ - (char*)new_indptr_);
         chunk_start_pos_ =
-            allocator.aligned_alloc<void>(padded_batch_size_after_partition * sizeof(IdType), 16);
+            allocator.aligned_alloc<void>(padded_batch_size * sizeof(IdType), 16);
         void* chunk_start_pos_h_ =
             (char*)page_locked_buffer_ + ((char*)chunk_start_pos_ - (char*)new_indptr_);
         seq_lengths_before_partition_ =
-            allocator.aligned_alloc<void>(padded_batch_size_after_partition * sizeof(IdType), 16);
+            allocator.aligned_alloc<void>(padded_batch_size * sizeof(IdType), 16);
         void* seq_lengths_before_partition_h_ =
             (char*)page_locked_buffer_ +
             ((char*)seq_lengths_before_partition_ - (char*)new_indptr_);
         block_valid_mask_ =
-            allocator.aligned_alloc<bool>(padded_batch_size_after_partition * sizeof(bool), 16);
+            allocator.aligned_alloc<bool>(padded_batch_size * sizeof(bool), 16);
         bool* block_valid_mask_h_ =
             (bool*)page_locked_buffer_ + ((bool*)block_valid_mask_ - (bool*)new_indptr_);
-        std::fill(block_valid_mask_h_, block_valid_mask_h_ + padded_batch_size_after_partition, 0);
+        std::fill(block_valid_mask_h_, block_valid_mask_h_ + padded_batch_size, 0);
 
         size_t num_bytes_to_copy = (char*)allocator.ptr - (char*)new_indptr_;
         FLASHINFER_CUDA_CALL(PartitionPagedKVCacheComputeAuxiliaryInfo(
-            max_num_pages_per_batch, batch_size, padded_batch_size_after_partition, page_size,
+            max_num_pages_per_batch, batch_size, padded_batch_size, page_size,
             indptr, last_page_len, (IdType*)new_indptr_h_, (IdType*)new_last_page_len_h_,
             (IdType*)chunk_indptr_h_, (IdType*)batch_idx_map_h_, (IdType*)chunk_start_pos_h_,
             (IdType*)seq_lengths_before_partition_h_, block_valid_mask_h_,
             /*device_buffer=*/new_indptr_,
             /*host_buffer=*/page_locked_buffer_, num_bytes_to_copy, stream_));
       } else {
         block_valid_mask_ = nullptr;
-        padded_batch_size_ = num_kv_heads * batch_size;
+        padded_batch_size_ = batch_size;
       }
     } else {
       // NOTE(Zihao): we don't use block_valid_mask when CUDAGraph is disabled.