linux-kernel - Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd reclaims at each priority

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Message-ID: <20130320161847.GD27375@dhcp22.suse.cz>
Date:	Wed, 20 Mar 2013 17:18:47 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Zlatko Calusic <zcalusic@...sync.net>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd
 reclaims at each priority

On Sun 17-03-13 13:04:07, Mel Gorman wrote:
[...]
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 88c5fed..4835a7a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2593,6 +2593,32 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
>  }
>  
>  /*
> + * kswapd shrinks the zone by the number of pages required to reach
> + * the high watermark.
> + */
> +static void kswapd_shrink_zone(struct zone *zone,
> +			       struct scan_control *sc,
> +			       unsigned long lru_pages)
> +{
> +	unsigned long nr_slab;
> +	struct reclaim_state *reclaim_state = current->reclaim_state;
> +	struct shrink_control shrink = {
> +		.gfp_mask = sc->gfp_mask,
> +	};
> +
> +	/* Reclaim above the high watermark. */
> +	sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));

OK, so the cap is at high watermark which sounds OK to me, although I
would expect balance_gap being considered here. Is it not used
intentionally or you just wanted to have a reasonable upper bound?

I am not objecting to that it just hit my eyes.

> +	shrink_zone(zone, sc);
> +
> +	reclaim_state->reclaimed_slab = 0;
> +	nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages);
> +	sc->nr_reclaimed += reclaim_state->reclaimed_slab;
> +
> +	if (nr_slab == 0 && !zone_reclaimable(zone))
> +		zone->all_unreclaimable = 1;
> +}
> +
> +/*
>   * For kswapd, balance_pgdat() will work across all this node's zones until
>   * they are all at high_wmark_pages(zone).
>   *
-- 
Michal Hocko
SUSE Labs
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