5.3 Node Access Policies

Maui allocates resources to jobs on the basis of a job task. As described in the glossary, a task is an atomic collection of resources which must be co-located on a single compute node. A given job may request 20 tasks where each task is defined as 'one processor and 128 MB of RAM'. Compute nodes with multiple processors often possess enough resources to support more than one task simultaneously. When it is possible for more than one task to run on a node, node access policies determine which tasks may share the compute nodes resources.

Maui supports four distinct node access policies which are listed in the table below.

Policy	Description
SHARED	Tasks from any combination of jobs may utilize available resources
SINGLEUSER	Tasks from any jobs owned by the same user may utilize available resources
SINGLEJOB	Tasks from a single job may utilize available resources
SINGLETASK	A single task from a single job may run on the node

Node Access polices may be specified via the parameter NODEACCESSPOLICY . The global default may be overridden using QOS flags or on a job-by-job basis using the resource manager extension NACCESSPOLICY . By default, nodes are accessible using the setting of the system wide NODEACCESSPOLICY parameter. However, jobs may override this policy and subsequent jobs are bound to conform to the access policies of all jobs currently running on a given node. For example, if the NODEACCESSPOLICY parameter was set to SHARED, a new job may be launched on an idle node with a job specific access policy of SINGLEUSER. While this job is running, subsequent job tasks may only be launched on this node provided they were submitted by the same user. When all single user jobs have completed on that node, the node can again be used in SHARED mode.