new system calls are added for cpusets - all support for querying and
modifying cpusets is via this cpuset file system.
-The /proc/<pid>/status file for each task has two added lines,
+The /proc/<pid>/status file for each task has four added lines,
displaying the tasks cpus_allowed (on which CPUs it may be scheduled)
and mems_allowed (on which Memory Nodes it may obtain memory),
-in the format seen in the following example:
+in the two formats seen in the following example:
Cpus_allowed: ffffffff,ffffffff,ffffffff,ffffffff
+ Cpus_allowed_list: 0-127
Mems_allowed: ffffffff,ffffffff
+ Mems_allowed_list: 0-63
Each cpuset is represented by a directory in the cgroup file system
containing (on top of the standard cgroup files) the following
( 4 : search nodes in a chunk of node [on NUMA system] )
( 5 : search system wide [on NUMA system] )
+The system default is architecture dependent. The system default
+can be changed using the relax_domain_level= boot parameter.
+
This file is per-cpuset and affect the sched domain where the cpuset
belongs to. Therefore if the flag 'sched_load_balance' of a cpuset
is disabled, then 'sched_relax_domain_level' have no effect since
There is an exception to the above. If hotplug functionality is used
to remove all the CPUs that are currently assigned to a cpuset,
-then the kernel will automatically update the cpus_allowed of all
-tasks attached to CPUs in that cpuset to allow all CPUs. When memory
-hotplug functionality for removing Memory Nodes is available, a
-similar exception is expected to apply there as well. In general,
-the kernel prefers to violate cpuset placement, over starving a task
-that has had all its allowed CPUs or Memory Nodes taken offline. User
-code should reconfigure cpusets to only refer to online CPUs and Memory
-Nodes when using hotplug to add or remove such resources.
+then all the tasks in that cpuset will be moved to the nearest ancestor
+with non-empty cpus. But the moving of some (or all) tasks might fail if
+cpuset is bound with another cgroup subsystem which has some restrictions
+on task attaching. In this failing case, those tasks will stay
+in the original cpuset, and the kernel will automatically update
+their cpus_allowed to allow all online CPUs. When memory hotplug
+functionality for removing Memory Nodes is available, a similar exception
+is expected to apply there as well. In general, the kernel prefers to
+violate cpuset placement, over starving a task that has had all
+its allowed CPUs or Memory Nodes taken offline.
There is a second exception to the above. GFP_ATOMIC requests are
kernel internal allocations that must be satisfied, immediately.