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Date: Thu, 2 Sep 2010 11:55:40 +0900
From: Minchan Kim <minchan.kim@...il.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: 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 Thu, Sep 2, 2010 at 9:57 AM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
>> 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.
Right. Thanks for pointing me out.
> I don't want to send risky patch to -stable.
Still I don't want to use oom_killer_disabled magic.
But I don't want to prevent urgent stable patch due to my just nitpick.
This is my last try(just quick patch, even I didn't tried compile test).
If this isn't good, first of all, let's try merge yours.
And then we can fix it later.
Thanks for comment.
-- CUT HERE --
Why do we check zone->all_unreclaimable in only kswapd?
If kswapd is freezed in hibernation, OOM can happen.
Let's the check in direct reclaim path, too.
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3109ff7..41493ba 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1878,12 +1878,11 @@ static void shrink_zone(int priority, struct zone *zone,
* If a zone is deemed to be full of pinned pages then just give it a light
* scan then give up on it.
*/
-static bool shrink_zones(int priority, struct zonelist *zonelist,
+static void shrink_zones(int priority, struct zonelist *zonelist,
struct scan_control *sc)
{
struct zoneref *z;
struct zone *zone;
- bool all_unreclaimable = true;
for_each_zone_zonelist_nodemask(zone, z, zonelist,
gfp_zone(sc->gfp_mask), sc->nodemask) {
@@ -1901,8 +1900,25 @@ static bool shrink_zones(int priority, struct
zonelist *zonelist,
}
shrink_zone(priority, zone, sc);
- all_unreclaimable = false;
}
+}
+
+static inline int all_unreclaimable(struct zonelist *zonelist, struct
scan_control *sc)
+{
+ struct zoneref *z;
+ struct zone *zone;
+ bool all_unreclaimable = true;
+
+ for_each_zone_zonelist_nodemask(zone, z, zonelist,
+ gfp_zone(sc->gfp_mask), sc->nodemask) {
+ if (!populated_zone(zone))
+ continue;
+ if (zone->pages_scanned < (zone_reclaimable_pages(zone) * 6)) {
+ all_unreclaimable = false;
+ break;
+ }
+ }
+
return all_unreclaimable;
}
@@ -1926,7 +1942,6 @@ static unsigned long do_try_to_free_pages(struct
zonelist *zonelist,
struct scan_control *sc)
{
int priority;
- bool all_unreclaimable;
unsigned long total_scanned = 0;
struct reclaim_state *reclaim_state = current->reclaim_state;
struct zoneref *z;
@@ -1943,7 +1958,7 @@ static unsigned long do_try_to_free_pages(struct
zonelist *zonelist,
sc->nr_scanned = 0;
if (!priority)
disable_swap_token();
- all_unreclaimable = shrink_zones(priority, zonelist, sc);
+ shrink_zones(priority, zonelist, sc);
/*
* Don't shrink slabs when reclaiming memory from
* over limit cgroups
@@ -2005,7 +2020,7 @@ out:
return sc->nr_reclaimed;
/* top priority shrink_zones still had more to do? don't OOM, then */
- if (scanning_global_lru(sc) && !all_unreclaimable)
+ if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
return 1;
return 0;
--
Kind regards,
Minchan Kim
View attachment "all_unreclaimable.patch" of type "text/x-diff" (2184 bytes)
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