linux-kernel - Re: [PATCH 04/10] mm: vmscan: Decide whether to compact the pgdat based on reclaim progress

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Date:	Tue, 19 Mar 2013 10:19:37 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
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>,
	Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/10] mm: vmscan: Decide whether to compact the pgdat
 based on reclaim progress

On Mon, Mar 18, 2013 at 07:11:30PM +0800, Wanpeng Li wrote:
> >@@ -2864,46 +2879,21 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
> > 		if (try_to_freeze() || kthread_should_stop())
> > 			break;
> >
> >-		/* If no reclaim progress then increase scanning priority */
> >-		if (sc.nr_reclaimed - nr_reclaimed == 0)
> >-			raise_priority = true;
> >+		/* Compact if necessary and kswapd is reclaiming efficiently */
> >+		this_reclaimed = sc.nr_reclaimed - nr_reclaimed;
> >+		if (order && pgdat_needs_compaction &&
> >+				this_reclaimed > nr_to_reclaim)
> >+			compact_pgdat(pgdat, order);
> >
> 
> Hi Mel,
> 
> If you should check compaction_suitable here to confirm it's not because
> other reasons like large number of pages under writeback to avoid blind
> compaction. :-)
> 

This starts as a question but it is not a question so I am not sure how
I should respond.

Checking compaction_suitable here is unnecessary because compact_pgdat()
makes the same check when it calls compact_zone().

-- 
Mel Gorman
SUSE Labs
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