Re: [patch 02/10] mm: memcontrol: rearrange charging fast path

From: Michal Hocko
Date: Tue Jun 03 2014 - 08:54:45 EST


On Thu 29-05-14 12:15:54, Johannes Weiner wrote:
> The charging path currently starts out with OOM condition checks when
> OOM is the rarest possible case.
>
> Rearrange this code to run OOM/task dying checks only after trying the
> percpu charge and the res_counter charge and bail out before entering
> reclaim. Attempting a charge does not hurt an (oom-)killed task as
> much as every charge attempt having to check OOM conditions. Also,
> only check __GFP_NOFAIL when the charge would actually fail.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Acked-by: Michal Hocko <mhocko@xxxxxxx>

> ---
> mm/memcontrol.c | 33 +++++++++++++++++----------------
> 1 file changed, 17 insertions(+), 16 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index c3c10ab98355..46b3e37542ad 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2576,22 +2576,6 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
>
> if (mem_cgroup_is_root(memcg))
> goto done;
> - /*
> - * Unlike in global OOM situations, memcg is not in a physical
> - * memory shortage. Allow dying and OOM-killed tasks to
> - * bypass the last charges so that they can exit quickly and
> - * free their memory.
> - */
> - if (unlikely(test_thread_flag(TIF_MEMDIE) ||
> - fatal_signal_pending(current) ||
> - current->flags & PF_EXITING))
> - goto bypass;
> -
> - if (unlikely(task_in_memcg_oom(current)))
> - goto nomem;
> -
> - if (gfp_mask & __GFP_NOFAIL)
> - oom = false;
> retry:
> if (consume_stock(memcg, nr_pages))
> goto done;
> @@ -2613,6 +2597,20 @@ retry:
> goto retry;
> }
>
> + /*
> + * Unlike in global OOM situations, memcg is not in a physical
> + * memory shortage. Allow dying and OOM-killed tasks to
> + * bypass the last charges so that they can exit quickly and
> + * free their memory.
> + */
> + if (unlikely(test_thread_flag(TIF_MEMDIE) ||
> + fatal_signal_pending(current) ||
> + current->flags & PF_EXITING))
> + goto bypass;
> +
> + if (unlikely(task_in_memcg_oom(current)))
> + goto nomem;
> +
> if (!(gfp_mask & __GFP_WAIT))
> goto nomem;
>
> @@ -2641,6 +2639,9 @@ retry:
> if (mem_cgroup_wait_acct_move(mem_over_limit))
> goto retry;
>
> + if (gfp_mask & __GFP_NOFAIL)
> + goto bypass;
> +
> if (fatal_signal_pending(current))
> goto bypass;
>
> --
> 1.9.3
>

--
Michal Hocko
SUSE Labs
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