Re: deferred rss update instead of sloppy rss

Andrew Morton
2004-11-22T23:16:28Z

Christoph Lameter <clameter@sgi.com> wrote:
>
> On Mon, 22 Nov 2004, Andrew Morton wrote:
>
> > > The page fault code only increments rss. For larger transactions that
> > > increase / decrease rss significantly the page_table_lock is taken and
> > > mm->rss is updated directly. So no
> > > gross inaccuracies can result.
> >
> > Sure. Take a million successive pagefaults and mm->rss is grossly
> > inaccurate. Hence my suggestion that it be spilled into mm->rss
> > periodically.
>
> It is spilled into mm->rss periodically. That is the whole point of the
> patch.
>
> The timer tick occurs every 1 ms.

That only works if the task happens to have the CPU when the timer tick
occurs. There remains no theoretical upper bound to the error in mm->rss,
and that's very easy to fix.