linux-kernel - Re: [PATCH] writeback: prevent bandwidth calculation overflow

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Message-ID: <4CE537BE.6090103@redhat.com>
Date:	Thu, 18 Nov 2010 09:27:10 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	"Li, Shaohua" <shaohua.li@...el.com>,
	Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	"Theodore Ts'o" <tytso@....edu>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mel@....ul.ie>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-mm <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] writeback: prevent bandwidth calculation overflow

On 11/18/2010 01:57 AM, Wu Fengguang wrote:
> On 32bit kernel, bdi->write_bandwidth can express at most 4GB/s.
>
> However the current calculation code can overflow when disk bandwidth
> reaches 800MB/s.  Fix it by using "long long" and swapping the order of
> multiplication/division. And further, change its unit to pages/second
> rather than bytes/second. That allows up to 16TB/s bandwidth in 32bit
> kernel.
>
> Signed-off-by: Wu Fengguang<fengguang.wu@...el.com>

Acked-by: Rik van Riel <riel@...hat.com>

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