From latest versions you can configure Oracle memory in different ways. I have to say that in very large environments and versions 10 and 11 the dynamic configuration can cause problems, so we must always look for hours with low activity or workload, or apply for a window of intervention to such operations. In small and medium systems this should not be a problem.
One time, attempting to increase SGA_TARGET from 8GB up to 10GB (SGA_MAX_SIZE = 10GB), by executing
alter system set sga_target = 6000M scope=both sid=’*’
After two hours, there is no “system altered returned” and MMAN process is busy 100% on cpu.
11520 is in this case multiple of the granule, if you configure a value not multiple of granule Oracle rounds it up. You can see the size of granule in the V$SGAINFO.
HTH – Antonio NAVARRO