fix too many copies (#2661)

Signed-off-by: Nshengjun.li <shengjun.li@zilliz.com>

core/src/index/knowhere/knowhere/index/vector_index/gpu/IndexGPUIVF.cpp

@@ -40,14 +40,11 @@ GPUIVF::Train(const DatasetPtr& dataset_ptr, const Config& config) {
         idx_config.device = gpu_id_;
         int32_t nlist = config[IndexParams::nlist];
         faiss::MetricType metric_type = GetMetricType(config[Metric::TYPE].get<std::string>());
-        faiss::gpu::GpuIndexIVFFlat device_index(gpu_res->faiss_res.get(), dim, nlist, metric_type, idx_config);
-        device_index.train(rows, (float*)p_data);
+        auto device_index =
+            new faiss::gpu::GpuIndexIVFFlat(gpu_res->faiss_res.get(), dim, nlist, metric_type, idx_config);
+        device_index->train(rows, (float*)p_data);
 
-        std::shared_ptr<faiss::Index> host_index = nullptr;
-        host_index.reset(faiss::gpu::index_gpu_to_cpu(&device_index));
-
-        auto device_index1 = faiss::gpu::index_cpu_to_gpu(gpu_res->faiss_res.get(), gpu_id_, host_index.get());
-        index_.reset(device_index1);
+        index_.reset(device_index);
         res_ = gpu_res;
     } else {
         KNOWHERE_THROW_MSG("Build IVF can't get gpu resource");

core/src/index/knowhere/knowhere/index/vector_index/gpu/IndexGPUIVFPQ.cpp

@@ -38,11 +38,8 @@ GPUIVFPQ::Train(const DatasetPtr& dataset_ptr, const Config& config) {
                                           config[IndexParams::m], config[IndexParams::nbits],
                                           GetMetricType(config[Metric::TYPE].get<std::string>()));  // IP not support
         device_index->train(rows, (float*)p_data);
-        std::shared_ptr<faiss::Index> host_index = nullptr;
-        host_index.reset(faiss::gpu::index_gpu_to_cpu(device_index));
 
-        auto device_index1 = faiss::gpu::index_cpu_to_gpu(gpu_res->faiss_res.get(), gpu_id_, host_index.get());
-        index_.reset(device_index1);
+        index_.reset(device_index);
         res_ = gpu_res;
     } else {
         KNOWHERE_THROW_MSG("Build IVFPQ can't get gpu resource");

core/src/index/knowhere/knowhere/index/vector_index/gpu/IndexIVFSQHybrid.cpp

@@ -45,19 +45,14 @@ IVFSQHybrid::Train(const DatasetPtr& dataset_ptr, const Config& config) {
         auto device_index = faiss::gpu::index_cpu_to_gpu(gpu_res->faiss_res.get(), gpu_id_, build_index);
         device_index->train(rows, (float*)p_data);
 
-        std::shared_ptr<faiss::Index> host_index = nullptr;
-        host_index.reset(faiss::gpu::index_gpu_to_cpu(device_index));
-
-        delete device_index;
-        delete build_index;
-
-        device_index = faiss::gpu::index_cpu_to_gpu(gpu_res->faiss_res.get(), gpu_id_, host_index.get());
         index_.reset(device_index);
         res_ = gpu_res;
         gpu_mode_ = 2;
     } else {
         KNOWHERE_THROW_MSG("Build IVFSQHybrid can't get gpu resource");
     }
+
+    delete build_index;
 }
 
 VecIndexPtr