Re: deferred rss update instead of sloppy rss

[Andrew Morton]

Christoph Lameter <clameter@xxxxxxx> 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.
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