Re: [PATCH 2/3 -mmotm-2009-12-10-17-19] Count zero page as file_rss

Hugh Dickins
2009-12-31T08:43:46Z

On Thu, 31 Dec 2009, Minchan Kim wrote:
> On Thu, Dec 31, 2009 at 1:49 AM, Hugh Dickins
> <hugh.dickins@tiscali.co.uk> wrote:
> >
> > You are right that I completely overlooked the issue of whether to
> > include the ZERO_PAGE in rss counts (now being a !vm_normal_page,
> > it was just natural to leave it out); and I overlooked the fact that
> > it used to be counted into file_rss in the old days (being !PageAnon).
> >
> > So I'm certainly at fault for that, and thank you for bringing the
> > issue to attention; but once considered, I can't actually see a good
> > reason why we should add code to count ZERO_PAGEs into file_rss now.
> > And if this patch falls, then 1/3 and 3/3 would fall also.
> >
> > And the patch below would be incomplete anyway, wouldn't it?
> > There would need to be a matching change to zap_pte_range(),
> > but I don't see that.
>
> Thanks.
> If we think this patch is need, I will repost path with fix it.
>
> What do you think?

If someone comes up with a convincing case in which their system
is behaving significantly worse because the zero page is not being
counted in rss now, then we shall probably want your patch.

But I still don't yet see a reason to add code just to keep the
anon_rss+file_rss number looking the same as it was before, in this
exceptional case where there's a significant number of zero pages.

Hugh