On Fri 30-11-12 17:31:24, Glauber Costa wrote:
> Currently, we rely on the cgroup_lock() to prevent changes to
> move_charge_at_immigrate during task migration. We can do something
> similar to what cpuset is doing, and flip a flag to tell us if task
> movement is taking place.
>
> In theory, we could busy loop waiting for that value to return to 0 - it
> will eventually. But I am judging that returning EAGAIN is not too much
> of a problem, since file writers already should be checking for error
> codes anyway.
I think we should prevent from EAGAIN because this is a behavior change.
Why not just loop with signal_pending test for breaking out and a small
sleep after attach_in_progress > 0 && unlock?
> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
> ---
> mm/memcontrol.c | 64 +++++++++++++++++++++++++++++++++++++++++++++------------
> 1 file changed, 51 insertions(+), 13 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index feba87d..d80b6b5 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -311,7 +311,13 @@ struct mem_cgroup {
> * Should we move charges of a task when a task is moved into this
> * mem_cgroup ? And what type of charges should we move ?
> */
> - unsigned long move_charge_at_immigrate;
> + unsigned long move_charge_at_immigrate;
> + /*
> + * Tasks are being attached to this memcg. Used mostly to prevent
> + * changes to move_charge_at_immigrate
> + */
> + int attach_in_progress;
> +
> /*
> * set > 0 if pages under this cgroup are moving to other cgroup.
> */
> @@ -4114,6 +4120,7 @@ static int mem_cgroup_move_charge_write(struct cgroup *cgrp,
> struct cftype *cft, u64 val)
> {
> struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> + int ret = -EAGAIN;
>
> if (val >= (1 << NR_MOVE_TYPE))
> return -EINVAL;
> @@ -4123,10 +4130,13 @@ static int mem_cgroup_move_charge_write(struct cgroup *cgrp,
> * inconsistent.
> */
> cgroup_lock();
> + if (memcg->attach_in_progress)
> + goto out;
> memcg->move_charge_at_immigrate = val;
> + ret = 0;
> +out:
> cgroup_unlock();
> -
> - return 0;
> + return ret;
> }
> #else
> static int mem_cgroup_move_charge_write(struct cgroup *cgrp,
> @@ -5443,12 +5453,12 @@ static void mem_cgroup_clear_mc(void)
> mem_cgroup_end_move(from);
> }
>
> -static int mem_cgroup_can_attach(struct cgroup *cgroup,
> - struct cgroup_taskset *tset)
> +
> +static int __mem_cgroup_can_attach(struct mem_cgroup *memcg,
> + struct cgroup_taskset *tset)
> {
> struct task_struct *p = cgroup_taskset_first(tset);
> int ret = 0;
> - struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
>
> if (memcg->move_charge_at_immigrate) {
> struct mm_struct *mm;
> @@ -5482,8 +5492,8 @@ static int mem_cgroup_can_attach(struct cgroup *cgroup,
> return ret;
> }
>
> -static void mem_cgroup_cancel_attach(struct cgroup *cgroup,
> - struct cgroup_taskset *tset)
> +static void __mem_cgroup_cancel_attach(struct mem_cgroup *memcg,
> + struct cgroup_taskset *tset)
> {
> mem_cgroup_clear_mc();
> }
> @@ -5630,8 +5640,8 @@ retry:
> up_read(&mm->mmap_sem);
> }
>
> -static void mem_cgroup_move_task(struct cgroup *cont,
> - struct cgroup_taskset *tset)
> +static void __mem_cgroup_move_task(struct mem_cgroup *memcg,
> + struct cgroup_taskset *tset)
> {
> struct task_struct *p = cgroup_taskset_first(tset);
> struct mm_struct *mm = get_task_mm(p);
> @@ -5645,20 +5655,48 @@ static void mem_cgroup_move_task(struct cgroup *cont,
> mem_cgroup_clear_mc();
> }
> #else /* !CONFIG_MMU */
> +static int __mem_cgroup_can_attach(struct mem_cgroup *memcg,
> + struct cgroup_taskset *tset)
> +{
> + return 0;
> +}
> +
> +static void __mem_cgroup_cancel_attach(struct mem_cgroup *memcg,
> + struct cgroup_taskset *tset)
> +{
> +}
> +
> +static void __mem_cgroup_move_task(struct mem_cgroup *memcg,
> + struct cgroup_taskset *tset)
> +{
> +}
> +#endif
> static int mem_cgroup_can_attach(struct cgroup *cgroup,
> struct cgroup_taskset *tset)
> {
> - return 0;
> + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
> +
> + memcg->attach_in_progress++;
> + return __mem_cgroup_can_attach(memcg, tset);
> }
> +
> static void mem_cgroup_cancel_attach(struct cgroup *cgroup,
> struct cgroup_taskset *tset)
> {
> + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
> +
> + __mem_cgroup_cancel_attach(memcg, tset);
> + memcg->attach_in_progress--;
> }
> -static void mem_cgroup_move_task(struct cgroup *cont,
> +
> +static void mem_cgroup_move_task(struct cgroup *cgroup,
> struct cgroup_taskset *tset)
> {
> + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
> +
> + __mem_cgroup_move_task(memcg, tset);
> + memcg->attach_in_progress--;
> }
> -#endif
>
> struct cgroup_subsys mem_cgroup_subsys = {
> .name = "memory",
> --
> 1.7.11.7
>
--
Michal Hocko
SUSE Labs
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