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

Minchan Kim
2010-01-04T00:47:13Z

On Mon, Jan 4, 2010 at 8:43 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Wed, 30 Dec 2009 16:49:52 +0000 (GMT)
> Hugh Dickins <hugh.dickins@tiscali.co.uk> wrote:
>
>> > >
>> > > Kame reported following as
>> > > "Before starting zero-page works, I checked "questions" in lkml and
>> > > found some reports that some applications start to go OOM after zero-page
>> > > removal.
>> > >
>> > > For me, I know one of my customer's application depends on behavior of
>> > > zero page (on RHEL5). So, I tried to add again it before RHEL6 because
>> > > I think removal of zero-page corrupts compatibility."
>> > >
>> > > So how about adding zero page as file_rss again for compatibility?
>>
>> I think not.
>>
>> KAMEZAWA-san can correct me (when he returns in the New Year) if I'm
>> wrong, but I don't think his customer's OOMs had anything to do with
>> whether the ZERO_PAGE was counted in file_rss or not: the OOMs came
>> from the fact that many pages were being used up where just the one
>> ZERO_PAGE had been good before.  Wouldn't he have complained if the
>> zero_pfn patches hadn't solved that problem?
>>
>> 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.
>>
>> We really don't want to be adding more and more ZERO_PAGE/zero_pfn
>> tests around the place if we can avoid them: KOSAKI-san has a strong
>> argument for adding such a test in kernel/futex.c, but I don't the
>> argument here.
>>
>
> I agree that ZERO_PAGE shouldn't be counted as rss. Now, I feel that old
> counting method(in old zero-page implementation) was bad.
>
> Minchan-san, I'm sorry for noise.

That's all right.
It was my mistake.

I will drop this and repost Matt and Hugh's ACK version.
Thanks for all. :)

>
> Thanks,
> -Kame
>
>
>
>

--
Kind regards,
Minchan Kim