Re: [patch] mm: adjust kswapd nice level for high priority page allocators

[Minchan Kim <minchan.kim@gmail.com>]

On Mon, Mar 1, 2010 at 7:14 PM, David Rientjes <rientjes@google.com> wrote:
> From: Con Kolivas <kernel@kolivas.org>
>
> When kswapd is awoken due to reclaim by a running task, set the priority
> of kswapd to that of the task allocating pages thus making memory reclaim
> cpu activity affected by nice level.
>
> [rientjes@google.com: refactor for current]
> Cc: Mel Gorman <mel@csn.ul.ie>
> Signed-off-by: Con Kolivas <kernel@kolivas.org>
> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  mm/vmscan.c |   33 ++++++++++++++++++++++++++++++++-
>  1 files changed, 32 insertions(+), 1 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1658,6 +1658,33 @@ static void shrink_zone(int priority, struct zone *zone,
>  }
>
>  /*
> + * Helper functions to adjust nice level of kswapd, based on the priority of
> + * the task allocating pages. If it is already higher priority we do not
> + * demote its nice level since it is still working on behalf of a higher
> + * priority task. With kernel threads we leave it at nice 0.
> + *
> + * We don't ever run kswapd real time, so if a real time task calls kswapd we
> + * set it to highest SCHED_NORMAL priority.
> + */
> +static int effective_sc_prio(struct task_struct *p)
> +{
> +       if (likely(p->mm)) {
> +               if (rt_task(p))
> +                       return -20;
> +               return task_nice(p);
> +       }
> +       return 0;
> +}
> +
> +static void set_kswapd_nice(struct task_struct *kswapd, int active)
> +{
> +       long nice = effective_sc_prio(current);
> +
> +       if (task_nice(kswapd) > nice || !active)
> +               set_user_nice(kswapd, nice);
> +}
> +
> +/*
>  * This is the direct reclaim path, for page-allocating processes.  We only
>  * try to reclaim pages from zones which will satisfy the caller's allocation
>  * request.
> @@ -2257,6 +2284,7 @@ static int kswapd(void *p)
>                                }
>                        }
>
> +                       set_user_nice(tsk, 0);

Why do you reset nice value which set by set_kswapd_nice?


-- 
Kind regards,
Minchan Kim

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