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Date:   Wed, 22 Sep 2021 15:13:01 +0100
From:   Mel Gorman <mgorman@techsingularity.net>
To:     Hillf Danton <hdanton@sina.com>
Cc:     Linux-MM <linux-mm@kvack.org>, NeilBrown <neilb@suse.de>,
        Dave Chinner <david@fromorbit.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/5] mm/vmscan: Throttle reclaim until some writeback
 completes if congested
Message-ID: <20210922141301.GZ3959@techsingularity.net>
References: <20210920085436.20939-1-mgorman@techsingularity.net>
 <20210922121620.4716-1-hdanton@sina.com>
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On Wed, Sep 22, 2021 at 08:16:20PM +0800, Hillf Danton wrote:
> On Mon, 20 Sep 2021 09:54:32 +0100 Mel Gorman wrote:
> > +static void
> > +reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason,
> > +							long timeout)
> > +{
> > +	wait_queue_head_t *wqh =3D &pgdat->reclaim_wait;
> > +	unsigned long start =3D jiffies;
> > +	long ret;
> > +	DEFINE_WAIT(wait);
> > +
> > +	atomic_inc(&pgdat->nr_reclaim_throttled);
> > +	WRITE_ONCE(pgdat->nr_reclaim_start,
> > +		 node_page_state(pgdat, NR_THROTTLED_WRITTEN));
> 
> Missing wakeup could happen if the current sleeper overwrites 
> pgdat->nr_reclaim_start set by the existing sleeper.
> 
> 	if (1 == atomic_inc_and_return(&pgdat->nr_reclaim_throttled))
> 		WRITE_ONCE(pgdat->nr_reclaim_start,
> 				node_page_state(pgdat, NR_THROTTLED_WRITTEN));
> 

Good spot, will fix.

-- 
Mel Gorman
SUSE Labs