linux-kernel - Re: [PATCH 4/5] writeback: per task dirty rate limit

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Date:	Tue, 9 Aug 2011 13:46:21 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	Greg Thelen <gthelen@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrea Righi <arighi@...eler.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] writeback: per task dirty rate limit

On Sat, Aug 06, 2011 at 04:44:51PM +0800, Wu Fengguang wrote:

[..]
>   * balance_dirty_pages() must be called by processes which are generating dirty
>   * data.  It looks at the number of dirty pages in the machine and will force
>   * the caller to perform writeback if the system is over `vm_dirty_ratio'.
> @@ -1008,6 +1005,9 @@ static void balance_dirty_pages(struct a
>  	if (clear_dirty_exceeded && bdi->dirty_exceeded)
>  		bdi->dirty_exceeded = 0;
>  
> +	current->nr_dirtied = 0;
> +	current->nr_dirtied_pause = ratelimit_pages(nr_dirty, dirty_thresh);
> +
>  	if (writeback_in_progress(bdi))
>  		return;
>  
> @@ -1034,8 +1034,6 @@ void set_page_dirty_balance(struct page 
>  	}
>  }
>  
> -static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
> -
>  /**
>   * balance_dirty_pages_ratelimited_nr - balance dirty memory state
>   * @mapping: address_space which was dirtied
> @@ -1055,30 +1053,17 @@ void balance_dirty_pages_ratelimited_nr(
>  {
>  	struct backing_dev_info *bdi = mapping->backing_dev_info;
>  	unsigned long ratelimit;
> -	unsigned long *p;
>  
>  	if (!bdi_cap_account_dirty(bdi))
>  		return;
>  
> -	ratelimit = ratelimit_pages;
> -	if (mapping->backing_dev_info->dirty_exceeded)
> +	ratelimit = current->nr_dirtied_pause;
> +	if (bdi->dirty_exceeded)
>  		ratelimit = 8;

Should we make sure that ratelimit is more than 8? It could be that
ratelimit is 1 and we set it higher (just reverse of what we wanted?)

Thanks
Vivek
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