Hi,
On 01/28/2013 02:54 PM, Jeff Liu wrote:
> As we don't account the swap stat number for the root_mem_cgroup anymore,
> here we can just return an invalid CSS ID if there is no non-root memcg
> is alive. Also, introduce memsw_accounting_users to track the number of
> active non-root memcgs.
>
> Signed-off-by: Jie Liu <jeff.liu@xxxxxxxxxx>
> CC: Glauber Costa <glommer@xxxxxxxxxxxxx>
> CC: Michal Hocko <mhocko@xxxxxxx>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> CC: Johannes Weiner <hannes@xxxxxxxxxxx>
> CC: Mel Gorman <mgorman@xxxxxxx>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> CC: Sha Zhengju <handai.szj@xxxxxxxxxx>
>
> ---
> mm/page_cgroup.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
> index c945254..189fbf5 100644
> --- a/mm/page_cgroup.c
> +++ b/mm/page_cgroup.c
> @@ -336,6 +336,8 @@ struct swap_cgroup {
> };
> #define SC_PER_PAGE (PAGE_SIZE/sizeof(struct swap_cgroup))
>
> +static atomic_t memsw_accounting_users = ATOMIC_INIT(0);
> +
I am not seeing this being incremented or decremented. I can only guess
that it comes in later patches. However, they are clearly used as a
global reference counter.
This is precisely one of the use cases static branches solve very
neatly. Did you consider using them?
True, they will help a lot more when we are touching hot paths, and swap
is hardly a hot path.
However, since one of the main complaints about memcg has been that we
inflict "death by a thousand cuts", maybe it wouldn't hurt everything
else being the same.
Michal and others, do you have any feelings here?
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