Re: [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx

[Hillf Danton]

On February 15, 2017 5:23 PM Mel Gorman wrote: 
>   */
>  static int kswapd(void *p)
>  {
> -	unsigned int alloc_order, reclaim_order, classzone_idx;
> +	unsigned int alloc_order, reclaim_order;
> +	unsigned int classzone_idx = MAX_NR_ZONES - 1;
>  	pg_data_t *pgdat = (pg_data_t*)p;
>  	struct task_struct *tsk = current;
> 
> @@ -3447,20 +3466,23 @@ static int kswapd(void *p)
>  	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
>  	set_freezable();
> 
> -	pgdat->kswapd_order = alloc_order = reclaim_order = 0;
> -	pgdat->kswapd_classzone_idx = classzone_idx = 0;
> +	pgdat->kswapd_order = 0;
> +	pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
>  	for ( ; ; ) {
>  		bool ret;
> 
> +		alloc_order = reclaim_order = pgdat->kswapd_order;
> +		classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
> +
>  kswapd_try_sleep:
>  		kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
>  					classzone_idx);
> 
>  		/* Read the new order and classzone_idx */
>  		alloc_order = reclaim_order = pgdat->kswapd_order;
> -		classzone_idx = pgdat->kswapd_classzone_idx;
> +		classzone_idx = kswapd_classzone_idx(pgdat, 0);
>  		pgdat->kswapd_order = 0;
> -		pgdat->kswapd_classzone_idx = 0;
> +		pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
> 
>  		ret = try_to_freeze();
>  		if (kthread_should_stop())
> @@ -3486,9 +3508,6 @@ static int kswapd(void *p)
>  		reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
>  		if (reclaim_order < alloc_order)
>  			goto kswapd_try_sleep;

If we fail order-5 request,  can we then give up order-5, and
try order-3 if requested, after napping?

> -
> -		alloc_order = reclaim_order = pgdat->kswapd_order;
> -		classzone_idx = pgdat->kswapd_classzone_idx;
>  	}
>