On Thu 23-10-14 10:33:50, Johannes Weiner wrote:
> mem_cgroup_end_move() checks if the passed memcg is NULL, along with a
> lengthy comment to explain why this seemingly non-sensical situation
> is even possible.
>
> Check in cancel_attach() itself whether can_attach() set up the move
> context or not, it's a lot more obvious from there. Then remove the
> check and comment in mem_cgroup_end_move().
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Acked-by: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/memcontrol.c | 10 +++-------
> 1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a5c9aa4688e8..3cd4f1e0bfb3 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1469,12 +1469,7 @@ static void mem_cgroup_start_move(struct mem_cgroup *memcg)
>
> static void mem_cgroup_end_move(struct mem_cgroup *memcg)
> {
> - /*
> - * Now, mem_cgroup_clear_mc() may call this function with NULL.
> - * We check NULL in callee rather than caller.
> - */
> - if (memcg)
> - atomic_dec(&memcg->moving_account);
> + atomic_dec(&memcg->moving_account);
> }
>
> /*
> @@ -5489,7 +5484,8 @@ static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
> static void mem_cgroup_cancel_attach(struct cgroup_subsys_state *css,
> struct cgroup_taskset *tset)
> {
> - mem_cgroup_clear_mc();
> + if (mc.to)
> + mem_cgroup_clear_mc();
> }
>
> static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
> --
> 2.1.2
>
--
Michal Hocko
SUSE Labs
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