ccNUMA Overview

Memory exhaustion and paging
The VM system has a strategy to allocate memory. The order in which localities are searched depends on the
memory object. Objects that desire interleaved memory will first search the interleaved locality and then perform a
round-robin search among all the local memory localities. Objects that desire cell local memory will first search
that local memory and then will search other localities in a closest-to-furthest order.
When no memory is available from the desired locality, the operating system will attempt to provide the “next
best” locality possible. If that locality also has no memory available, then the next best will be chosen, and so on,
until the entire system has been searched. It is important to remember that requests for a particular locality of
memory are always hints, never guarantees.
When memory is exhausted and a page must be paged out, the VM system has a similar strategy when it must
page it back in. The VM system will use the same policy it used originally to choose the locality to start its
allocation task.
Page migration
Page migration is not supported directly. In the case of memory exhaustion, memory pages may be paged to
backing storage (swap space). When it is paged back in, it will use the same heuristics to determine where
physical memory should come from. If the process has migrated from one LDOM to another LDOM, the parts of
the process that desire cell local memory will first look in the cell local memory of the new LDOM.
Summary
HP-UX 11i v2 provides application developers with a comprehensive set of tools to maximize performance on the
HP Integrity servers. Most applications will be able to exploit the system with no changes, and applications that do
need to change have a complete set of tools to manage data locality and the execution domain.
References
HP-UX SCA Programming and Process Management, Version 1.0, October 18, 1999.
VM ccNUMA: Physical Memory Allocation and Page Placement, Design Overview & Specification, Version 1.3.
HP-UX Variable Page-size for IA Design Overview & Specification, May 16, 2002.
HP-UX PM ccNUMA Investigation Report, Version 0.2, Harshad Parekh and Anushree Ramakrishnan.
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