From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id 21D376B0071 for ; Fri, 19 Nov 2010 11:07:00 -0500 (EST) Date: Fri, 19 Nov 2010 17:06:53 +0100 From: Michal Hocko Subject: Re: [PATCH] writeback: prevent bandwidth calculation overflow Message-ID: <20101119160653.GB3871@tiehlicka.suse.cz> References: <20101118065725.GB8458@localhost> <4CE537BE.6090103@redhat.com> <20101118154408.GA18582@localhost> <1290096121.2109.1525.camel@laptop> <20101118161356.GA20569@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101118161356.GA20569@localhost> Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: Peter Zijlstra , Rik van Riel , Andrew Morton , Jan Kara , "Li, Shaohua" , Christoph Hellwig , Dave Chinner , Theodore Ts'o , Chris Mason , Mel Gorman , KOSAKI Motohiro , linux-mm , "linux-fsdevel@vger.kernel.org" , LKML List-ID: On Fri 19-11-10 00:13:56, Wu Fengguang wrote: > On Fri, Nov 19, 2010 at 12:02:01AM +0800, Peter Zijlstra wrote: > > On Thu, 2010-11-18 at 23:44 +0800, Wu Fengguang wrote: > > > + pause = HZ * pages_dirtied / (bw + 1); > > > > Shouldn't that be using something like div64_u64 ? > > Thanks for review. Here is the updated patch using div64_u64(). > > --- > Subject: writeback: prevent bandwidth calculation overflow > Date: Thu Nov 18 12:55:42 CST 2010 > > 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 div64_u64() in the > calculations. > > And further change its unit from bytes/second to pages/second. > That allows up to 16TB/s bandwidth in 32bit kernel. > > CC: Peter Zijlstra > Acked-by: Rik van Riel > Signed-off-by: Wu Fengguang > --- > mm/backing-dev.c | 4 ++-- > mm/page-writeback.c | 11 +++++------ > 2 files changed, 7 insertions(+), 8 deletions(-) > > --- linux-next.orig/mm/page-writeback.c 2010-11-18 12:42:58.000000000 +0800 > +++ linux-next/mm/page-writeback.c 2010-11-19 00:08:23.000000000 +0800 > @@ -494,7 +494,7 @@ void bdi_update_write_bandwidth(struct b > unsigned long written; > unsigned long elapsed; > unsigned long bw; > - unsigned long w; > + unsigned long long w; > > if (*bw_written == 0) > goto snapshot; > @@ -513,7 +513,7 @@ void bdi_update_write_bandwidth(struct b > goto snapshot; > > written = percpu_counter_read(&bdi->bdi_stat[BDI_WRITTEN]) - *bw_written; > - bw = (HZ * PAGE_CACHE_SIZE * written + elapsed/2) / elapsed; > + bw = (HZ * written + elapsed/2) / elapsed; Sorry for a dumb question, but where did PAGE_CACHE_SIZE part go? > w = min(elapsed / unit_time, 128UL); > bdi->write_bandwidth = (bdi->write_bandwidth * (1024-w) + bw * w) >> 10; > bdi->write_bandwidth_update_time = jiffies; -- Michal Hocko L3 team SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org