linux-kernel - [PATCH -v2] cpuset: hotplug documentation fix

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Message-ID: <48C0BFA9.2000200@cn.fujitsu.com>
Date:	Fri, 05 Sep 2008 13:12:09 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	akpm@...ux-foundation.org
CC:	Paul Jackson <pj@....com>, menage@...gle.com,
	linux-kernel@...r.kernel.org, jh@....com
Subject: [PATCH -v2] 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@...fujitsu.com>
Acked-by: Paul Jackson <pj@....com>
---

fixed a typo: s/binded/bound

--
 Documentation/cpusets.txt |   18 ++++++++++--------
 1 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 1f5a924..47e568a 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -635,14 +635,16 @@ prior 'mems' setting, will not be moved.
 
 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.
-- 
1.5.4.rc3

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