On Mon 28-01-13 18:54:40, 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);
Nobody manipulates whith this number. I suspect the next patch will do
but it is generally better to have also users of the introduced counters
in the same patch. For one thing this patch would introduce a regression
because no pages would be accounted at this stage (for example during
git bisect).
> +
> /*
> * SwapCgroup implements "lookup" and "exchange" operations.
> * In typical usage, this swap_cgroup is accessed via memcg's charge/uncharge
> @@ -389,6 +391,9 @@ static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
> struct page *mappage;
> struct swap_cgroup *sc;
>
> + if (!atomic_read(&memsw_accounting_users))
> + return NULL;
> +
> ctrl = &swap_cgroup_ctrl[swp_type(ent)];
> if (ctrlp)
> *ctrlp = ctrl;
> @@ -416,6 +421,8 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
> unsigned short retval;
>
> sc = lookup_swap_cgroup(ent, &ctrl);
> + if (!sc)
> + return 0;
>
> spin_lock_irqsave(&ctrl->lock, flags);
> retval = sc->id;
> @@ -443,6 +450,8 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
> unsigned long flags;
>
> sc = lookup_swap_cgroup(ent, &ctrl);
> + if (!sc)
> + return 0;
>
> spin_lock_irqsave(&ctrl->lock, flags);
> old = sc->id;
> @@ -460,7 +469,9 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
> */
> unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
> {
> - return lookup_swap_cgroup(ent, NULL)->id;
> + struct swap_cgroup *sc = lookup_swap_cgroup(ent, NULL);
> +
> + return sc ? sc->id : 0;
> }
>
> int swap_cgroup_swapon(int type, unsigned long max_pages)
> @@ -471,6 +482,9 @@ int swap_cgroup_swapon(int type, unsigned long max_pages)
> if (!do_swap_account)
> return 0;
>
> + if (!atomic_read(&memsw_accounting_users))
> + return 0;
> +
> length = DIV_ROUND_UP(max_pages, SC_PER_PAGE);
>
> ctrl = &swap_cgroup_ctrl[type];
> --
> 1.7.9.5
>
> --
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--
Michal Hocko
SUSE Labs
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