linux-kernel - Re: [PATCH 13/19] mm/migrate: Use xchg instead of spinlock

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Message-ID: <1528136558.7898.115.camel@surriel.com>
Date:   Mon, 04 Jun 2018 14:22:38 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 13/19] mm/migrate: Use xchg instead of spinlock

On Mon, 2018-06-04 at 15:30 +0530, Srikar Dronamraju wrote:
> 
> +++ b/mm/migrate.c
> @@ -1874,11 +1874,9 @@ static bool
> numamigrate_update_ratelimit(pg_data_t *pgdat,
>  	 * all the time is being spent migrating!
>  	 */
>  	if (time_after(jiffies, pgdat-
> >numabalancing_migrate_next_window)) {
> -		spin_lock(&pgdat->numabalancing_migrate_lock);
> -		pgdat->numabalancing_migrate_nr_pages = 0;
> -		pgdat->numabalancing_migrate_next_window = jiffies +
> -			msecs_to_jiffies(migrate_interval_millisecs)
> ;
> -		spin_unlock(&pgdat->numabalancing_migrate_lock);
> +		if (xchg(&pgdat->numabalancing_migrate_nr_pages, 0))
> +			pgdat->numabalancing_migrate_next_window =
> jiffies +
> +				msecs_to_jiffies(migrate_interval_mi
> llisecs);
>  	}

I am not convinced this is simpler, but no real
objection either way :)

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