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 <a.p.zijlstra@xxxxxxxxx> > Acked-by: Rik van Riel <riel@xxxxxxxxxx> > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > --- > 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@xxxxxxxxxx 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: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>