linux-kernel - Re: [PATCH 08/10] mm: vmscan: Have kswapd shrink slab only once per priority

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Message-ID: <51669091.5070406@gmail.com>
Date:	Thu, 11 Apr 2013 18:29:37 +0800
From:	Ric Mason <ric.masonn@...il.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	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>,
	Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/10] mm: vmscan: Have kswapd shrink slab only once per
 priority

Hi Mel,
On 04/11/2013 06:01 PM, Mel Gorman wrote:
> On Wed, Apr 10, 2013 at 02:21:42PM +0900, Joonsoo Kim wrote:
>>>>> @@ -2673,9 +2674,15 @@ static bool kswapd_shrink_zone(struct zone *zone,
>>>>>   	sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
>>>>>   	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;
>>>>> +	/*
>>>>> +	 * Slabs are shrunk for each zone once per priority or if the zone
>>>>> +	 * being balanced is otherwise unreclaimable
>>>>> +	 */
>>>>> +	if (shrinking_slab || !zone_reclaimable(zone)) {
>>>>> +		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;
>>>> Why shrink_slab() is called here?
>>> Preserves existing behaviour.
>> Yes, but, with this patch, existing behaviour is changed, that is, we call
>> shrink_slab() once per priority. For now, there is no reason this function
>> is called here. How about separating it and executing it outside of
>> zone loop?
>>
> We are calling it fewer times but it's still receiving the same information
> from sc->nr_scanned it received before. With the change you are suggesting
> it would be necessary to accumulating sc->nr_scanned for each zone shrunk
> and then pass the sum to shrink_slab() once per priority. While this is not
> necessarily wrong, there is little or no motivation to alter the shrinkers
> in this manner in this series.

Why the result is not the same?


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