How can improve the performance and handle the large amounts of data with Report Viewer

You have to use the EnableVirtualEvaluation and DisablePageSplitting in ReportViewerController.cs to handle the larger amount data. This will helpful to process the report with less memory footprint

public void OnInitReportOptions(ReportViewerOptions reportOption)
{
    reportOption.ReportModel.EnableVirtualEvaluation = true;
    reportOption.ReportModel.DisablePageSplitting = true;
}

To improve the loading performance, you are requesting to set CanGrow true for necessary textbox alone in report. Because, if you set the CanGrow for textboxes and report having larger amount, then viewer will takes time, measure, height, and width for each textbox cells based on amount of data.

See Also

Render report with huge data in Reportserver