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Subject[-mm][PATCH 4/4] Add rlimit controller documentation


This is the documentation patch. It describes the rlimit controller and how
to build and use it.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---
Documentation/controllers/rlimit.txt | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff -puN /dev/null Documentation/controllers/rlimit.txt
--- /dev/null 2008-05-03 22:12:13.033285313 +0530
+++ linux-2.6.25-balbir/Documentation/controllers/rlimit.txt 2008-05-04 03:06:06.000000000 +0530
@@ -0,0 +1,29 @@
+This controller is enabled by the CONFIG_CGROUP_RLIMIT_CTLR option. Prior
+to reading this documentation please read Documentation/cgroups.txt and
+Documentation/controllers/memory.txt. Several of the principles of this
+controller are similar to the memory resource controller.
+
+This controller framework is designed to be extensible to control any
+resource limit (memory related) with little effort.
+
+This new controller, controls the address space expansion of the tasks
+belonging to a cgroup. Address space control is provided along the same lines as
+RLIMIT_AS control, which is available via getrlimit(2)/setrlimit(2).
+The interface for controlling address space is provided through
+"rlimit.limit_in_bytes". The file is similar to "limit_in_bytes" w.r.t. the user
+interface. Please see section 3 of the memory resource controller documentation
+for more details on how to use the user interface to get and set values.
+
+The "rlimit.usage_in_bytes" file provides information about the total address
+space usage of the tasks in the cgroup, in bytes.
+
+Advantages of providing this feature
+
+1. Control over virtual address space allows for a cgroup to fail gracefully
+ i.e., via a malloc or mmap failure as compared to OOM kill when no
+ pages can be reclaimed.
+2. It provides better control over how many pages can be swapped out when
+ the cgroup goes over its limit. A badly setup cgroup can cause excessive
+ swapping. Providing control over the address space allocations ensures
+ that the system administrator has control over the total swapping that
+ can take place.
_
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL


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