cgroups: make swap accounting default behavior configurable

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).  If the option is selected
then the feature is turned on by default.

It also adds a new boot parameter swapaccount[=1|0] which enhances the
original noswapaccount parameter semantic by means of enable/disable logic
(defaults to 1 if no value is provided to be still consistent with
noswapaccount).

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@suse.cz>
Acked-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: 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, 13 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 88c10468db46..c9728992a776 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 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 noswapaccount does the trick).
 
 menuconfig CGROUP_SCHED
         bool "Group CPU scheduler"