Re: [PATCH 3/5] vmscan: Force kswapd to take notice faster when high-order watermarks are being hit

[KOSAKI Motohiro]

> When a high-order allocation fails, kswapd is kicked so that it reclaims
> at a higher-order to avoid direct reclaimers stall and to help GFP_ATOMIC
> allocations. Something has changed in recent kernels that affect the timing
> where high-order GFP_ATOMIC allocations are now failing with more frequency,
> particularly under pressure. This patch forces kswapd to notice sooner that
> high-order allocations are occuring.
> 
> Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
> ---
>  mm/vmscan.c |    9 +++++++++
>  1 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 64e4388..cd68109 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2016,6 +2016,15 @@ loop_again:
>  					priority != DEF_PRIORITY)
>  				continue;
>  
> +			/*
> +			 * Exit quickly to restart if it has been indicated
> +			 * that higher orders are required
> +			 */
> +			if (pgdat->kswapd_max_order > order) {
> +				all_zones_ok = 1;
> +				goto out;
> +			}
> +
>  			if (!zone_watermark_ok(zone, order,
>  					high_wmark_pages(zone), end_zone, 0))
>  				all_zones_ok = 0;

this is simplest patch and seems reasonable.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro>


btw, now balance_pgdat() have too complex flow. at least Vincent was
confused it.
Then, I think kswap_max_order handling should move into balance_pgdat()
at later release.
the following patch addressed my proposed concept.