[PATCH] Make swap accounting default behavior configurable

[Michal Hocko]

Swap accounting can be configured by CONFIG_CGROUP_MEM_RES_CTLR_SWAP
configuration option and then it is turned on by default. There is
a boot option (noswapaccount) which can disable this feature.

This makes it hard for distributors to enable the configuration option
as this feature leads to a bigger memory consumption and this is a no-go
for general purpose distribution kernel. On the other hand swap
accounting may be very usuful for some workloads.

This patch adds a new configuration option which controls the default
behavior (CGROUP_MEM_RES_CTLR_SWAP_ENABLED) and changes the original
noswapaccount parameter to swapaccount=true|false which provides
a more fine grained way to control this feature.

The default behavior is unchanged (if CONFIG_CGROUP_MEM_RES_CTLR_SWAP is
enabled then CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED is enabled as well)

Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
---
 init/Kconfig    |   13 +++++++++++++
 mm/memcontrol.c |   19 ++++++++++++++-----
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 88c1046..61d55a7 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -613,6 +613,19 @@ config CGROUP_MEM_RES_CTLR_SWAP
 	  if boot option "noswapaccount" is set, swap will not be accounted.
 	  Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
 	  size is 4096bytes, 512k per 1Gbytes of swap.
+config CGROUP_MEM_RES_CTLR_SWAP_ENABLED
+	bool "Memory Resource Controller Swap Extension enabled by default"
+	depends on CGROUP_MEM_RES_CTLR_SWAP
+	default y
+	help
+	  Memory Resource Controller Swap Extension comes with its price in
+	  a bigger memory consumption. General purpose distribution kernels
+	  which want to enable the feautre but keep it disabled by default
+	  and let the user enable it by swapaccount=true boot command line
+	  parameter should have this option unselected.
+	  For those who want to have the feature enabled by default should
+	  select this option (if, for some reason, they need to disable it
+	  then swapaccount=false does the trick).
 
 menuconfig CGROUP_SCHED
 	bool "Group CPU scheduler"
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9a99cfa..7c699b3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -61,7 +61,14 @@ struct mem_cgroup *root_mem_cgroup __read_mostly;
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
 /* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */
 int do_swap_account __read_mostly;
-static int really_do_swap_account __initdata = 1; /* for remember boot option*/
+
+/* for remember boot option*/
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP_ENABLED
+static int really_do_swap_account __initdata = 1;
+#else
+static int really_do_swap_account __initdata = 0;
+#endif
+
 #else
 #define do_swap_account		(0)
 #endif
@@ -4909,11 +4916,13 @@ struct cgroup_subsys mem_cgroup_subsys = {
 };
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
-
-static int __init disable_swap_account(char *s)
+static int __init enable_swap_account(char *s)
 {
-	really_do_swap_account = 0;
+	if (!s || !strcmp(s, "true"))
+		really_do_swap_account = 1;
+	else if (!strcmp(s, "false"))
+		really_do_swap_account = 0;
 	return 1;
 }
-__setup("noswapaccount", disable_swap_account);
+__setup("swapaccount", enable_swap_account);
 #endif
-- 
1.7.2.3


-- 
Michal Hocko
L3 team 
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
--
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