Re: deferred rss update instead of sloppy rss

Christoph Lameter
2004-11-22T22:48:22Z

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. The maximum pagefault frequency that I
have seen is 500000 faults /second. The max deviation is therefore
less than 500 (could be greater if page table lock / mmap_sem always held
when the tick occurs).