Here we would like to draw your attention to GL21 transaction code in SAP. As we know it is being used in the SAP FI-SL (Special Purpose Ledger in FI) component which is coming under FI module (Financial Accounting). GL21 is a transaction code used for Create rollup in SAP.
It comes under the package for FI-SL rollup (GBRU). When we execute this transaction code, SAPMGLRE is the normal standard SAP program that is being executed in background. Transaction code GL21 is included in the SAP component for SAP_FIN.
Transaction GL21 technical data table