Linux Kernel 2.2

Linux 2.2 does not yet have a suitable mechanism (such as shm_open) for using the new memory management function. For this reason, if you are using Linux 2.2, you have to use the old memory management function.

Note the following restrictions.

  • A signed integer defines the maximum size of a shared memory segment. This has the effect that if you require more than 2 GB, you will need more than one segment.
  • Linux 2.2 can administrate a maximum of 4 GB of physical memory. Computers with main memory in excess of 4 GB cannot use their additional memory under Linux 2.2.
  • A system configuration that causes high paging rates can bring any operating system to a standstill. This is because the system is permanently occupied with swapping pages in and out. Unlike Linux 2.4, Linux 2.2 does not gradually slow down as the load increases. Instead, it can suddenly enter a swapping-only state, excluding all other tasks. This behavior is known as "thrashing".

Therefore, with Linux 2.2, keep an eye on the paging rates!

This means that the size of both the extended memory and the available virtual memory (physical storage space and swap space) is severely limited.

SAP therefore recommends that you implement the following configuration on Linux kernel 2.2:

  • The sum total of all SAP buffers and user contexts may not exceed 2.2 GB. This sum should also not be much greater than the physical main memory.
  • See note 103747 for recommendations on the SAP buffer settings.
  • Restrict the EM usage of an individual user context using parameter ztta/roll_extension. (You have already determined the total size em/initial_size_MB in accordance with the first point above.)
  • You should configure the SAP instance so that excessive swapping is avoided. If the database is running on the same machine, make sure that resources on the machine are not running thin. Check the dynamically allocated heap memory, using the parameters abap/heap_area_dia, abap/heap_area_nondia, and abap/heap_area_total.