linux-kernel - [-mm][PATCH 4/4] Add rlimit controller documentation

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Message-Id: <20080503213825.3140.4328.sendpatchset@localhost.localdomain>
Date:	Sun, 04 May 2008 03:08:25 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	linux-mm@...ck.org
Cc:	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
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@...ux.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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