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Subject: Re: [PATCH 05/10] writeback: per task dirty rate limit
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: linux-fsdevel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
        Jan Kara <jack@suse.cz>, Christoph Hellwig <hch@lst.de>,
        Dave Chinner <david@fromorbit.com>, Greg Thelen <gthelen@google.com>,
        Minchan Kim <minchan.kim@gmail.com>, Vivek Goyal <vgoyal@redhat.com>,
        Andrea Righi <arighi@develer.com>, linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Date: Fri, 26 Aug 2011 14:51:09 +0200
In-Reply-To: <20110826114619.268843347@intel.com>
References: <20110826113813.895522398@intel.com>
	 <20110826114619.268843347@intel.com>
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On Fri, 2011-08-26 at 19:38 +0800, Wu Fengguang wrote:
> +       preempt_disable();
>         /*
> -        * Check the rate limiting. Also, we do not want to throttle real-time
> -        * tasks in balance_dirty_pages(). Period.
> +        * This prevents one CPU to accumulate too many dirtied pages without
> +        * calling into balance_dirty_pages(), which can happen when there are
> +        * 1000+ tasks, all of them start dirtying pages at exactly the same
> +        * time, hence all honoured too large initial task->nr_dirtied_pause.
>          */
> -       preempt_disable();
>         p =  &__get_cpu_var(bdp_ratelimits);

	p = &get_cpu_var(bdp_ratelimits);

> -       *p += nr_pages_dirtied;
> -       if (unlikely(*p >= ratelimit)) {
> -               ratelimit = sync_writeback_pages(*p);
> +       if (unlikely(current->nr_dirtied >= ratelimit))
>                 *p = 0;
> -               preempt_enable();
> -               balance_dirty_pages(mapping, ratelimit);
> -               return;
> +       else {
> +               *p += nr_pages_dirtied;
> +               if (unlikely(*p >= ratelimit_pages)) {
> +                       *p = 0;
> +                       ratelimit = 0;
> +               }
>         }
>         preempt_enable(); 

	put_cpu_var(bdp_ratelimits);