Re: [PATCH] vmscan: scan pages until it founds eligible pages

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] vmscan: scan pages until it founds eligible pages
Date	2017-05-10 09:30 +0200
Message-ID	<tFuem-6dd-5@gated-at.bofh.it> (permalink)
References	(5 earlier) <tCUoG-8jC-9@gated-at.bofh.it> <tCVE6-105-27@gated-at.bofh.it> <tFoVj-1uw-1@gated-at.bofh.it> <tFt8C-5Ab-19@gated-at.bofh.it> <tFtV0-65D-5@gated-at.bofh.it>
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On Wed 10-05-17 16:03:11, Minchan Kim wrote:
> On Wed, May 10, 2017 at 08:13:12AM +0200, Michal Hocko wrote:
> > On Wed 10-05-17 10:46:54, Minchan Kim wrote:
> > > On Wed, May 03, 2017 at 08:00:44AM +0200, Michal Hocko wrote:
[...]
> > > > +		scan++;
> > > >  		switch (__isolate_lru_page(page, mode)) {
> > > >  		case 0:
> > > >  			nr_pages = hpage_nr_pages(page);
> > > 
> > > Confirmed.
> > 
> > Hmm. I can clearly see how we could skip over too many pages and hit
> > small reclaim priorities too quickly but I am still scratching my head
> > about how we could hit the OOM killer as a result. The amount of pages
> > on the active anonymous list suggests that we are not able to rotate
> > pages quickly enough. I have to keep thinking about that.
> 
> I explained it but seems to be not enouggh. Let me try again.
> 
> The problem is that get_scan_count determines nr_to_scan with
> eligible zones.
> 
>         size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
>         size = size >> sc->priority;

Ohh, right. Who has done that ;) Now it is much more clear. We simply
reclaimed all the pages on the inactive LRU list and only very slowly
progress over active list and hit the OOM before we can actually reach
anything. I completely forgot about the scan window not being the full
LRU list.

Thanks for bearing with me!
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH] vmscan: scan pages until it founds eligible pages Minchan Kim <minchan@kernel.org> - 2017-05-02 07:20 +0200
  Re: [PATCH] vmscan: scan pages until it founds eligible pages Michal Hocko <mhocko@kernel.org> - 2017-05-02 10:00 +0200
    Re: [PATCH] vmscan: scan pages until it founds eligible pages Minchan Kim <minchan@kernel.org> - 2017-05-02 17:00 +0200
      Re: [PATCH] vmscan: scan pages until it founds eligible pages Michal Hocko <mhocko@kernel.org> - 2017-05-02 17:20 +0200
        Re: [PATCH] vmscan: scan pages until it founds eligible pages Minchan Kim <minchan@kernel.org> - 2017-05-03 06:50 +0200
          Re: [PATCH] vmscan: scan pages until it founds eligible pages Michal Hocko <mhocko@kernel.org> - 2017-05-03 08:10 +0200
            Re: [PATCH] vmscan: scan pages until it founds eligible pages Minchan Kim <minchan@kernel.org> - 2017-05-10 03:50 +0200
              Re: [PATCH] vmscan: scan pages until it founds eligible pages Michal Hocko <mhocko@kernel.org> - 2017-05-10 08:20 +0200
                Re: [PATCH] vmscan: scan pages until it founds eligible pages Minchan Kim <minchan@kernel.org> - 2017-05-10 09:10 +0200
                Re: [PATCH] vmscan: scan pages until it founds eligible pages Michal Hocko <mhocko@kernel.org> - 2017-05-10 09:30 +0200

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