Re: [PATCH 22/34] mm, page_alloc: wake kswapd based on the highest eligible zone

[Vlastimil Babka]

On 07/08/2016 11:34 AM, Mel Gorman wrote:
> The ac_classzone_idx is used as the basis for waking kswapd and that is based
> on the preferred zoneref. If the preferred zoneref's first zone is lower
> than what is available on other nodes, it's possible that kswapd is woken
> on a zone with only higher, but still eligible, zones. As classzone_idx
> is strictly adhered to now, it causes a problem because eligible pages
> are skipped.
>
> For example, node 0 has only DMA32 and node 1 has only NORMAL. An allocating
> context running on node 0 may wake kswapd on node 1 telling it to skip
> all NORMAL pages.
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bb261885c121..e6ee52f1c15f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3415,7 +3415,7 @@ static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac)
>  	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
>  					ac->high_zoneidx, ac->nodemask) {
>  		if (last_pgdat != zone->zone_pgdat)
> -			wakeup_kswapd(zone, order, ac_classzone_idx(ac));
> +			wakeup_kswapd(zone, order, ac->high_zoneidx);
>  		last_pgdat = zone->zone_pgdat;
>  	}
>  }