cpuset: hotplug documentation fix
If all the cpus in a cpuset are offlined, the tasks in it will be moved to the nearest ancestor with non-empty cpus. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Acked-by: Paul Jackson <pj@sgi.com> Cc: Paul Menage <menage@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -635,14 +635,16 @@ prior 'mems' setting, will not be moved.
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There is an exception to the above. If hotplug functionality is used
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to remove all the CPUs that are currently assigned to a cpuset,
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then the kernel will automatically update the cpus_allowed of all
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tasks attached to CPUs in that cpuset to allow all CPUs. When memory
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hotplug functionality for removing Memory Nodes is available, a
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similar exception is expected to apply there as well. In general,
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the kernel prefers to violate cpuset placement, over starving a task
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that has had all its allowed CPUs or Memory Nodes taken offline. User
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code should reconfigure cpusets to only refer to online CPUs and Memory
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Nodes when using hotplug to add or remove such resources.
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then all the tasks in that cpuset will be moved to the nearest ancestor
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with non-empty cpus. But the moving of some (or all) tasks might fail if
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cpuset is bound with another cgroup subsystem which has some restrictions
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on task attaching. In this failing case, those tasks will stay
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in the original cpuset, and the kernel will automatically update
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their cpus_allowed to allow all online CPUs. When memory hotplug
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functionality for removing Memory Nodes is available, a similar exception
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is expected to apply there as well. In general, the kernel prefers to
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violate cpuset placement, over starving a task that has had all
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its allowed CPUs or Memory Nodes taken offline.
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There is a second exception to the above. GFP_ATOMIC requests are
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kernel internal allocations that must be satisfied, immediately.
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