Shared memory

You can configure your system so that multiple logical partitions share a pool of physical memory. A shared memory environment includes the shared memory pool, logical partitions that use the shared memory in the shared memory pool, logical memory, I/O entitled memory, at least one Virtual I/O Server logical partition, and paging space devices.

Overview of shared memory
Shared memory is physical memory that is assigned to the shared memory pool and shared among multiple logical partitions. The shared memory pool is a defined collection of physical memory blocks that are managed as a single memory pool by the hypervisor. Logical partitions that you configure to use shared memory (hereafter referred to as shared memory partitions) share the memory in the pool with other shared memory partitions.
Data flow for shared memory partitions
When the operating system that runs in a logical partition that uses shared memory (hereafter referred to as a shared memory partition) needs to access data, the data must reside in the shared memory pool. Systems with overcommitted memory configurations require the hypervisor and at least one Virtual I/O Server (VIOS) logical partition that is assigned to the shared memory pool (hereafter referred to as paging VIOS partition) to move data between the shared memory pool and the paging space devices as needed.
Logical memory
Logical memory is the address space, assigned to a logical partition, that the operating system perceives as its main storage. For a logical partition that uses shared memory (hereafter referred to as a shared memory partition), a subset of the logical memory is backed up by physical main storage and the remaining logical memory is kept in auxiliary storage.
I/O entitled memory
I/O entitled memory is the maximum amount of physical memory (from the shared memory pool) that is guaranteed to be available to a logical partition that uses shared memory (hereafter referred to as a shared memory partition) for its I/O devices at any given time.
Paging VIOS partition
A Virtual I/O Server (VIOS) logical partition that is assigned to the shared memory pool (hereafter referred to as a paging VIOS partition) provides access to the paging space devices for the logical partitions that are assigned to the shared memory pool (hereafter referred to as shared memory partitions).
Paging space device
You can learn about how the Hardware Management Console (HMC) and Integrated Virtualization Manager allocate and manipulate paging space devices on systems that use shared memory.
Shared memory distribution
The hypervisor uses the memory weight of each logical partition that uses shared memory (hereafter referred to as shared memory partitions) to help determine which logical partitions receive more physical memory from the shared memory pool. To help optimize performance and memory use, the operating systems that run in shared memory partitions provide the hypervisor with information about how the operating system uses its memory to help the hypervisor determine which pages to store in the shared memory pool and which pages to store in the paging space devices.

Parent topic: Memory

Related concepts

Performance considerations for shared memory partitions

Sharing resources between logical partitions

Related tasks

Configuring the shared memory pool

Creating logical partitions

Managing the shared memory pool

Managing shared memory dynamically

Related information

Defining the shared memory pool by using the Integrated Virtualization Manager

Configuring the management partition and client logical partitions

Managing the shared memory pool by using the Integrated Virtualization Manager

Dynamically managing memory by using the Integrated Virtualization Manager