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

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Message-ID: <alpine.LSU.2.00.0912310833560.26642@sister.anvils>
Date:	Thu, 31 Dec 2009 08:43:39 +0000 (GMT)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Minchan Kim <minchan.kim@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 2/3 -mmotm-2009-12-10-17-19] Count zero page as
 file_rss

On Thu, 31 Dec 2009, Minchan Kim wrote:
> On Thu, Dec 31, 2009 at 1:49 AM, Hugh Dickins
> <hugh.dickins@...cali.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
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