Re: [PATCH] writeback: prevent bandwidth calculation overflow

[Wu Fengguang]

On Fri, Nov 19, 2010 at 12:29:00AM +0800, Peter Zijlstra wrote:
> On Fri, 2010-11-19 at 00:06 +0800, 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 ?
> > 
> > OK, but a dumb question: gcc cannot handle this implicitly?
> 
> it could, but we chose not to implement the symbol it emits for these
> things so as to cause pain.. that was still assuming the world of 32bit
> computing was relevant and 64bit divides were expensive ;-)

Good to know that, thanks!  So let's avoid it totally :)
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