[RFC][3/3] Update documentation for virtual address space control (v2)

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Changelog v2
------------
Fix typos and implement review suggestions from Randy

This patch adds documentation for virtual address space control.

Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
---

 Documentation/controllers/memory.txt |   28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff -puN Documentation/controllers/memory.txt~memory-controller-virtual-address-control-documentation Documentation/controllers/memory.txt
--- linux-2.6.25-rc5/Documentation/controllers/memory.txt~memory-controller-virtual-address-control-documentation	2008-03-27 00:18:19.000000000 +0530
+++ linux-2.6.25-rc5-balbir/Documentation/controllers/memory.txt	2008-03-27 00:18:19.000000000 +0530
@@ -237,7 +237,33 @@ cgroup might have some charge associated
 tasks have migrated away from it. Such charges are automatically dropped at
 rmdir() if there are no tasks.
 
-5. TODO
+5. Virtual address space accounting
+
+A new resource counter controls the address space expansion of the tasks in
+the 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
+"as_limit_in_bytes". The file is similar to "limit_in_bytes" w.r.t. the user
+interface. Please see section 3 for more details on how to use the user
+interface to get and set values.
+
+The "as_usage_in_bytes" file provides information about the total address
+space usage of the cgroup in bytes.
+
+5.1 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.
+
+NOTE: This feature is controlled by the CONFIG_CGROUP_MEM_RES_CTLR_AS
+
+6. TODO
 
 1. Add support for accounting huge pages (as a separate controller)
 2. Make per-cgroup scanner reclaim not-shared pages first
_

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL

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