Memory controller improve user interface

Change the interface to use bytes instead of pages.  Page sizes can vary
across platforms and configurations.  A new strategy routine has been added
to the resource counters infrastructure to format the data as desired.

Suggested by David Rientjes, Andrew Morton and Herbert Poetzl

Tested on a UML setup with the config for memory control enabled.

[kamezawa.hiroyu@jp.fujitsu.com: possible race fix in res_counter]
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelianov <xemul@openvz.org>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: David Rientjes <rientjes@google.com>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 24 insertions, 5 deletions

diff --git a/Documentation/controllers/memory.txt b/Documentation/controllers/memory.txt
index 7e27baacca7b..61df8f81c803 100644
--- a/Documentation/controllers/memory.txt
+++ b/Documentation/controllers/memory.txt
@@ -165,11 +165,30 @@ c. Enable CONFIG_CGROUP_MEM_CONT
 
 Since now we're in the 0 cgroup,
 We can alter the memory limit:
-# echo -n 6000 > /cgroups/0/memory.limit
+# echo -n 4M > /cgroups/0/memory.limit_in_bytes
+
+NOTE: We can use a suffix (k, K, m, M, g or G) to indicate values in kilo,
+mega or gigabytes.
+
+# cat /cgroups/0/memory.limit_in_bytes
+4194304 Bytes
+
+NOTE: The interface has now changed to display the usage in bytes
+instead of pages
 
 We can check the usage:
-# cat /cgroups/0/memory.usage
-25
+# cat /cgroups/0/memory.usage_in_bytes
+1216512 Bytes
+
+A successful write to this file does not guarantee a successful set of
+this limit to the value written into the file.  This can be due to a
+number of factors, such as rounding up to page boundaries or the total
+availability of memory on the system.  The user is required to re-read
+this file after a write to guarantee the value committed by the kernel.
+
+# echo -n 1 > memory.limit_in_bytes
+# cat memory.limit_in_bytes
+4096 Bytes
 
 The memory.failcnt field gives the number of times that the cgroup limit was
 exceeded.
@@ -206,8 +225,8 @@ cgroup might have some charge associated with it, even though all
 tasks have migrated away from it. If some pages are still left, after following
 the steps listed in sections 4.1 and 4.2, check the Swap Cache usage in
 /proc/meminfo to see if the Swap Cache usage is showing up in the
-cgroups memory.usage counter. A simple test of swapoff -a and swapon -a
-should free any pending Swap Cache usage.
+cgroups memory.usage_in_bytes counter. A simple test of swapoff -a and
+swapon -a should free any pending Swap Cache usage.
 
 4.4 Choosing what to account  -- Page Cache (unmapped) vs RSS (mapped)?