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

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

On Tue, Mar 2, 2010 at 1:02 AM, Minchan Kim <minchan.kim@gmail.com> wrote:
> 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?

My point is that you reset nice value(which is boosted at wakeup_kswapd) to 0
before calling balance_pgdat. It means kswapd could be rescheduled by nice 0
before really reclaim happens by balance_pgdat.
I think it would invalidate your goal which kswapd's priority can be inherited
by direct reclaimed process's one.

What am I missing now?

>
> --
> Kind regards,
> Minchan Kim
>



-- 
Kind regards,
Minchan Kim

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