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

From: Hillf Danton
Date: Thu Feb 16 2017 - 01:23:38 EST


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;
> }
>