Re: [patch v2] mm, memcg: periodically schedule when emptying page list

[Michal Hocko]

On Mon 02-06-14 17:51:25, David Rientjes wrote:
> From: Hugh Dickins <hughd@xxxxxxxxxx>
> 
> mem_cgroup_force_empty_list() can iterate a large number of pages on an lru and 
> mem_cgroup_move_parent() doesn't return an errno unless certain criteria, none 
> of which indicate that the iteration may be taking too long, is met.
> 
> We have encountered the following stack trace many times indicating
> "need_resched set for > 51000020 ns (51 ticks) without schedule", for example:
> 
> 	scheduler_tick()
> 	<timer irq>
> 	mem_cgroup_move_account+0x4d/0x1d5
> 	mem_cgroup_move_parent+0x8d/0x109
> 	mem_cgroup_reparent_charges+0x149/0x2ba
> 	mem_cgroup_css_offline+0xeb/0x11b
> 	cgroup_offline_fn+0x68/0x16b
> 	process_one_work+0x129/0x350
> 
> If this iteration is taking too long, we still need to do cond_resched() even 
> when an individual page is not busy.
> 
> [rientjes@xxxxxxxxxx: changelog]
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxx>

Thanks!

> ---
>  v2: always reschedule if needed, "page" itself may not have a pc mismatch
>      or been unable to isolate.
> 
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4784,9 +4784,9 @@ static void mem_cgroup_force_empty_list(struct mem_cgroup *memcg,
>  		if (mem_cgroup_move_parent(page, pc, memcg)) {
>  			/* found lock contention or "pc" is obsolete. */
>  			busy = page;
> -			cond_resched();
>  		} else
>  			busy = NULL;
> +		cond_resched();
>  	} while (!list_empty(list));
>  }
>  

-- 
Michal Hocko
SUSE Labs
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