linux-kernel - Re: [PATCH v5 3/9] writeback: convert variables to unsigned

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Date:	Mon, 28 Feb 2011 01:07:21 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	containers@...ts.osdl.org, Andrea Righi <arighi@...eler.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Ciju Rajan K <ciju@...ux.vnet.ibm.com>,
	David Rientjes <rientjes@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Chad Talbott <ctalbott@...gle.com>,
	Justin TerAvest <teravest@...gle.com>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH v5 3/9] writeback: convert variables to unsigned

On Fri, Feb 25, 2011 at 01:35:54PM -0800, Greg Thelen wrote:
> Convert two balance_dirty_pages() page counter variables (nr_reclaimable
> and nr_writeback) from 'long' to 'unsigned long'.
> 
> These two variables are used to store results from global_page_state().
> global_page_state() returns unsigned long and carefully sums per-cpu
> counters explicitly avoiding returning a negative value.
> 
> Signed-off-by: Greg Thelen <gthelen@...gle.com>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

> ---
> Changelog since v4:
> - Created this patch for clarity.  Previously this patch was integrated within
>   the "writeback: create dirty_info structure" patch.
> 
>  mm/page-writeback.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 2cb01f6..4408e54 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -478,8 +478,10 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
>  static void balance_dirty_pages(struct address_space *mapping,
>  				unsigned long write_chunk)
>  {
> -	long nr_reclaimable, bdi_nr_reclaimable;
> -	long nr_writeback, bdi_nr_writeback;
> +	unsigned long nr_reclaimable;
> +	long bdi_nr_reclaimable;
> +	unsigned long nr_writeback;
> +	long bdi_nr_writeback;
>  	unsigned long background_thresh;
>  	unsigned long dirty_thresh;
>  	unsigned long bdi_thresh;
> -- 
> 1.7.3.1
> 
bdi_nr_[reclaimable|writeback] can return negative value?
When I just look through bdi_stat_sum, it uses *percpu_counter_sum_positive*.
So I guess it always returns positive value. 
If it is right, could you change it, too?

-- 
Kind regards,
Minchan Kim
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