> On Wed, Mar 23, 2011 at 5:44 PM, KOSAKI Motohiro
> <kosaki.motohiro@xxxxxxxxxxxxxx> wrote:
> >> > Boo.
> >> > You seems forgot why you introduced current all_unreclaimable() function.
> >> > While hibernation, we can't trust all_unreclaimable.
> >>
> >> Hmm. AFAIR, the why we add all_unreclaimable is when the hibernation is going on,
> >> kswapd is freezed so it can't mark the zone->all_unreclaimable.
> >> So I think hibernation can't be a problem.
> >> Am I miss something?
> >
> > Ahh, I missed. thans correct me. Okay, I recognized both mine and your works.
> > Can you please explain why do you like your one than mine?
>
> Just _simple_ :)
> I don't want to change many lines although we can do it simple and very clear.
>
> >
> > btw, Your one is very similar andrey's initial patch. If your one is
> > better, I'd like to ack with andrey instead.
>
> When Andrey sent a patch, I though this as zone_reclaimable() is right
> place to check it than out of zone_reclaimable. Why I didn't ack is
> that Andrey can't explain root cause but you did so you persuade me.
>
> I don't mind if Andrey move the check in zone_reclaimable and resend
> or I resend with concrete description.
>
> Anyway, most important thing is good description to show the root cause.
> It is applied to your patch, too.
> You should have written down root cause in description.
honestly, I really dislike to use mixing zone->pages_scanned and
zone->all_unreclaimable. because I think it's no simple. I don't
think it's good taste nor easy to review. Even though you who VM
expert didn't understand this issue at once, it's smell of too
mess code.
therefore, I prefore to take either 1) just remove the function or
2) just only check zone->all_unreclaimable and oom_killer_disabled
instead zone->pages_scanned.
And, I agree I need to rewrite the description.
How's this?
==================================================
>From 216bcf3fb0476b453080debf8999c74c635ed72f Mon Sep 17 00:00:00 2001
From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Date: Sun, 8 May 2011 17:39:44 +0900
Subject: [PATCH] vmscan: remove all_unreclaimable check from direct reclaim path completely
all_unreclaimable check in direct reclaim has been introduced at 2.6.19
by following commit.
2006 Sep 25; commit 408d8544; oom: use unreclaimable info
And it went through strange history. firstly, following commit broke
the logic unintentionally.
2008 Apr 29; commit a41f24ea; page allocator: smarter retry of
costly-order allocations
Two years later, I've found obvious meaningless code fragment and
restored original intention by following commit.
2010 Jun 04; commit bb21c7ce; vmscan: fix do_try_to_free_pages()
return value when priority==0
But, the logic didn't works when 32bit highmem system goes hibernation
and Minchan slightly changed the algorithm and fixed it .
2010 Sep 22: commit d1908362: vmscan: check all_unreclaimable
in direct reclaim path
But, recently, Andrey Vagin found the new corner case. Look,
struct zone {
..
int all_unreclaimable;
..
unsigned long pages_scanned;
..
}
zone->all_unreclaimable and zone->pages_scanned are neigher atomic
variables nor protected by lock. Therefore zones can become a state
of zone->page_scanned=0 and zone->all_unreclaimable=1. In this case,
current all_unreclaimable() return false even though
zone->all_unreclaimabe=1.
Is this ignorable minor issue? No. Unfortunatelly, x86 has very
small dma zone and it become zone->all_unreclamble=1 easily. and
if it become all_unreclaimable=1, it never restore all_unreclaimable=0.
Why? if all_unreclaimable=1, vmscan only try DEF_PRIORITY reclaim and
a-few-lru-pages>>DEF_PRIORITY always makes 0. that mean no page scan
at all!
Eventually, oom-killer never works on such systems. Let's remove
this problematic logic completely.
Reported-by: Andrey Vagin <avagin@xxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxxxx>
Cc: Minchan Kim <minchan.kim@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
---
mm/vmscan.c | 36 +-----------------------------------
1 files changed, 1 insertions(+), 35 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 060e4c1..254aada 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1989,33 +1989,6 @@ static bool zone_reclaimable(struct zone *zone)
}
/*
- * As hibernation is going on, kswapd is freezed so that it can't mark
- * the zone into all_unreclaimable. It can't handle OOM during hibernation.
- * So let's check zone's unreclaimable in direct reclaim as well as kswapd.
- */
-static bool 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 (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
- continue;
- if (zone_reclaimable(zone)) {
- all_unreclaimable = false;
- break;
- }
- }
-
- return all_unreclaimable;
-}
-
-/*
* This is the main entry point to direct page reclaim.
*
* If a full scan of the inactive list fails to free enough memory then we
@@ -2105,14 +2078,7 @@ out:
delayacct_freepages_end();
put_mems_allowed();
- if (sc->nr_reclaimed)
- return sc->nr_reclaimed;
-
- /* top priority shrink_zones still had more to do? don't OOM, then */
- if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
- return 1;
-
- return 0;
+ return sc->nr_reclaimed;
}
unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
--
1.6.5.2
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