Due to 32 bit virtual address limitations workarounds have been implemented in Linux to increase the maximum size for shared memories. The workaround is to lower the Mapped Base Address (
mapped_base) for shared libraries and the SGA Attach Address for shared memory segments. Lowering the Mapped Base Address and the SGA Attach Address allows SGA sizes up to 2.7 GB. By default, the shared memory segment size can only be increased to roughly 1.7 GB in Red Hat Enterprise Linux 2.1.
To better understand the process of lowering the Mapped Base Address for shared libraries and the SGA Attach Address for shared memory segments, a basic understanding of the Linux memory layout is necessary.