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Date: Thu, 2 Sep 2010 09:57:35 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: Minchan Kim <minchan.kim@...il.com> Cc: kosaki.motohiro@...fujitsu.com, Johannes Weiner <hannes@...xchg.org>, Rik van Riel <riel@...hat.com>, "Rafael J. Wysocki" <rjw@...k.pl>, "M. Vefa Bicakci" <bicave@...eronline.com>, LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [BUGFIX][PATCH] vmscan: don't use return value trick when oom_killer_disabled > On Wed, Sep 01, 2010 at 11:01:43AM +0900, Minchan Kim wrote: > > On Wed, Sep 1, 2010 at 10:55 AM, KOSAKI Motohiro > > <kosaki.motohiro@...fujitsu.com> wrote: > > > Hi > > > > > > Thank you for good commenting! > > > > > > > > >> I don't like use oom_killer_disabled directly. > > >> That's because we have wrapper inline functions to handle the > > >> variable(ex, oom_killer_[disable/enable]). > > >> It means we are reluctant to use the global variable directly. > > >> So should we make new function as is_oom_killer_disable? > > >> > > >> I think NO. > > >> > > >> As I read your description, this problem is related to only hibernation. > > >> Since hibernation freezes all processes(include kswapd), this problem > > >> happens. Of course, now oom_killer_disabled is used by only > > >> hibernation. But it can be used others in future(Off-topic : I don't > > >> want it). Others can use it without freezing processes. Then kswapd > > >> can set zone->all_unreclaimable and the problem can't happen. > > >> > > >> So I want to use sc->hibernation_mode which is already used > > >> do_try_to_free_pages instead of oom_killer_disabled. > > > > > > Unfortunatelly, It's impossible. shrink_all_memory() turn on > > > sc->hibernation_mode. but other hibernation caller merely call > > > alloc_pages(). so we don't have any hint. > > > > > Ahh.. True. Sorry for that. > > I will think some better method. > > if I can't find it, I don't mind this patch. :) > > It seems that the poblem happens following as. > (I might miss something since I just read theyour description) > > hibernation > oom_disable > alloc_pages > do_try_to_free_pages > if (scanning_global_lru(sc) && !all_unreclaimable) > return 1; > If kswapd is not freezed, it would set zone->all_unreclaimable to 1 and then > shrink_zones maybe return true. so alloc_pages could go to _nopage_. > If it is, it's no problem. > Right? > > I think the problem would come from shrink_zones. > It set false to all_unreclaimable blindly even though shrink_zone can't reclaim > any page. It doesn't make sense. > How about this? > I think we need this regardless of the problem. > What do you think about? > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index d8fd87d..22017b3 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1901,7 +1901,8 @@ static bool shrink_zones(int priority, struct zonelist *zonelist, > } > > shrink_zone(priority, zone, sc); > - all_unreclaimable = false; > + if (sc->nr_reclaimed) > + all_unreclaimable = false; > } > return all_unreclaimable; > } here is brief of shrink_zones(). for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(sc->gfp_mask), sc->nodemask) { if (!populated_zone(zone)) continue; if (zone->all_unreclaimable && priority != DEF_PRIORITY) continue; /* Let kswapd poll it */ shrink_zone(priority, zone, sc); all_unreclaimable = false; } That said, all zone's zone->all_unreclaimable are true -> all_unreclaimable local variable become true. otherwise -> all_unreclaimable local variable become false. The intention is, we don't want to invoke oom-killer if there are !all_unreclaimable zones. So your patch makes big design change and seems to increase OOM risk. I don't want to send risky patch to -stable. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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