linux-kernel - Re: [PATCH 08/27] mm, vmscan: Make kswapd reclaim in terms of nodes

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Date:	Sun, 28 Feb 2016 11:16:44 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Mel Gorman <mgorman@...hsingularity.net>
Cc:	Linux-MM <linux-mm@...ck.org>, Rik van Riel <riel@...riel.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/27] mm, vmscan: Make kswapd reclaim in terms of nodes

On Tue, Feb 23, 2016 at 03:04:31PM +0000, Mel Gorman wrote:
> @@ -3299,20 +3191,37 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
>  			break;
>  
>  		/*
> +		 * Stop reclaiming if any eligible zone is balanced and clear
> +		 * node writeback or congested.
> +		 */
> +		for (i = 0; i <= classzone_idx; i++) {
> +			zone = pgdat->node_zones + i;
> +			if (!populated_zone(zone))
> +				continue;
> +
> +			if (zone_balanced(zone, sc.order, 0, classzone_idx)) {
> +				clear_bit(PGDAT_CONGESTED, &pgdat->flags);
> +				clear_bit(PGDAT_DIRTY, &pgdat->flags);
> +				goto out;
> +			}
> +		}
> +
> +		/*
>  		 * Raise priority if scanning rate is too low or there was no
>  		 * progress in reclaiming pages
>  		 */
>  		if (raise_priority || !sc.nr_reclaimed)
>  			sc.priority--;
> -	} while (sc.priority >= 1 &&
> -			!pgdat_balanced(pgdat, order, classzone_idx));
> +	} while (sc.priority >= 1);
>  
>  out:
>  	/*
> -	 * Return the highest zone idx we were reclaiming at so
> -	 * prepare_kswapd_sleep() makes the same decisions as here.
> +	 * Return the order we were reclaiming at so prepare_kswapd_sleep()
> +	 * makes a decision on the order we were last reclaiming at. However,
> +	 * if another caller entered the allocator slow path while kswapd
> +	 * was awake, order will remain at the higher level
>  	 */
> -	return end_zone;
> +	return order;

It's sc.order that's updated based on fragmentation, not order.

There is also a now-stale comment above the function saying it returns
the highest reclaimed zone index.

Otherwise, the patch looks good to me.

Acked-by: Johannes Weiner <hannes@...xchg.org>