Re: [PATCH v2 3/6] memcg: introduce memsw_accounting_users

[Lord Glauber Costa of Sealand <glommer@parallels.com>]

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@oracle.com>
> CC: Glauber Costa <glommer@parallels.com>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Mel Gorman <mgorman@suse.de>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: Sha Zhengju <handai.szj@taobao.com>
> 
> ---
>  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?

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>