Re: [PATCH] cleanup kswapd()

[Mel Gorman]

On Sun, Nov 14, 2010 at 06:05:26PM +0900, KOSAKI Motohiro wrote:
> 
> Currently, kswapd() function has deeper nest and it slightly harder to
> read. cleanup it.
> 
> Cc: Mel Gorman <mel@xxxxxxxxx>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> ---
>  mm/vmscan.c |   71 +++++++++++++++++++++++++++++++---------------------------
>  1 files changed, 38 insertions(+), 33 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 8cc90d5..82ffe5f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2364,6 +2364,42 @@ out:
>  	return sc.nr_reclaimed;
>  }
>  
> +void kswapd_try_to_sleep(pg_data_t *pgdat, int order)
> +{

As pointed out elsewhere, this should be static.

> +	long remaining = 0;
> +	DEFINE_WAIT(wait);
> +
> +	if (freezing(current) || kthread_should_stop())
> +		return;
> +
> +	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
> +
> +	/* Try to sleep for a short interval */
> +	if (!sleeping_prematurely(pgdat, order, remaining)) {
> +		remaining = schedule_timeout(HZ/10);
> +		finish_wait(&pgdat->kswapd_wait, &wait);
> +		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
> +	}
> +
> +	/*
> +	 * After a short sleep, check if it was a
> +	 * premature sleep. If not, then go fully
> +	 * to sleep until explicitly woken up
> +	 */

Very minor but that comment should now fit on fewer lines.

> +	if (!sleeping_prematurely(pgdat, order, remaining)) {
> +		trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
> +		set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
> +		schedule();
> +		set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);

I posted a patch adding a comment on why set_pgdat_percpu_threshold() is
called. I do not believe it has been picked up by Andrew but it if is,
the patches will conflict. The resolution will be obvious but you may
need to respin this patch if the comment patch gets picked up in mmotm.

Otherwise, I see no problems.

> +	} else {
> +		if (remaining)
> +			count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
> +		else
> +			count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
> +	}
> +	finish_wait(&pgdat->kswapd_wait, &wait);
> +}
> +
>  /*
>   * The background pageout daemon, started as a kernel thread
>   * from the init process.
> @@ -2382,7 +2418,7 @@ static int kswapd(void *p)
>  	unsigned long order;
>  	pg_data_t *pgdat = (pg_data_t*)p;
>  	struct task_struct *tsk = current;
> -	DEFINE_WAIT(wait);
> +
>  	struct reclaim_state reclaim_state = {
>  		.reclaimed_slab = 0,
>  	};
> @@ -2414,7 +2450,6 @@ static int kswapd(void *p)
>  		unsigned long new_order;
>  		int ret;
>  
> -		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
>  		new_order = pgdat->kswapd_max_order;
>  		pgdat->kswapd_max_order = 0;
>  		if (order < new_order) {
> @@ -2424,39 +2459,9 @@ static int kswapd(void *p)
>  			 */
>  			order = new_order;
>  		} else {
> -			if (!freezing(current) && !kthread_should_stop()) {
> -				long remaining = 0;
> -
> -				/* Try to sleep for a short interval */
> -				if (!sleeping_prematurely(pgdat, order, remaining)) {
> -					remaining = schedule_timeout(HZ/10);
> -					finish_wait(&pgdat->kswapd_wait, &wait);
> -					prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
> -				}
> -
> -				/*
> -				 * After a short sleep, check if it was a
> -				 * premature sleep. If not, then go fully
> -				 * to sleep until explicitly woken up
> -				 */
> -				if (!sleeping_prematurely(pgdat, order, remaining)) {
> -					trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
> -					set_pgdat_percpu_threshold(pgdat,
> -						calculate_normal_threshold);
> -					schedule();
> -					set_pgdat_percpu_threshold(pgdat,
> -						calculate_pressure_threshold);
> -				} else {
> -					if (remaining)
> -						count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
> -					else
> -						count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
> -				}
> -			}
> -
> +			kswapd_try_to_sleep(pgdat, order);
>  			order = pgdat->kswapd_max_order;
>  		}
> -		finish_wait(&pgdat->kswapd_wait, &wait);
>  
>  		ret = try_to_freeze();
>  		if (kthread_should_stop())
> -- 
> 1.6.5.2
> 
> 
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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