linux-kernel - Re: [PATCH 5/6] mm: page_alloc: Reduce cost of dirty zone balancing

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Message-Id: <20140625163528.11368b86ef7d0a38cf9d1255@linux-foundation.org>
Date:	Wed, 25 Jun 2014 16:35:28 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-FSDevel <linux-fsdevel@...r.kernel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Jens Axboe <axboe@...nel.dk>, Jeff Moyer <jmoyer@...hat.com>,
	Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH 5/6] mm: page_alloc: Reduce cost of dirty zone balancing

On Wed, 25 Jun 2014 08:58:48 +0100 Mel Gorman <mgorman@...e.de> wrote:

> @@ -325,7 +321,14 @@ static unsigned long zone_dirty_limit(struct zone *zone)
>   */
>  bool zone_dirty_ok(struct zone *zone)
>  {
> -	unsigned long limit = zone_dirty_limit(zone);
> +	unsigned long limit = zone->dirty_limit_cached;
> +	struct task_struct *tsk = current;
> +
> +	if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
> +		limit = zone_dirty_limit(zone);
> +		zone->dirty_limit_cached = limit;
> +		limit += limit / 4;
> +	}

Could we get a comment in here explaining what we're doing and why
PF_LESS_THROTTLE and rt_task control whether we do it?

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