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.
|Tasks from any combination of jobs may utilize available
|Tasks from any jobs owned by the same user may utilize
|Tasks from a single job may utilize available resources
|A single task from a single job may run on the node
Node Access polices may be specified via the parameter
. The global default may be overridden using QOS flags or on a job-by-job
basis using the resource manager extension
. 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.