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vmscan: all_unreclaimable() use zone->all_unreclaimable as a name

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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.

This resulted in the kernel hanging up when executing a loop of the form

1. fork
2. mmap
3. touch memory
4. read memory
5. munmmap

as described in
1348725 (1348725)

Is this ignorable minor issue?  No.  Unfortunately, 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.  That said, we can't
use zone->pages_scanned for this purpose.  This patch restore
all_unreclaimable() use zone->all_unreclaimable as old.  and in addition,
to add oom_killer_disabled check to avoid reintroduce the issue of commit
d1908362 ("vmscan: check all_unreclaimable in direct reclaim path").

Reported-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Nick Piggin <npiggin@kernel.dk>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KOSAKI Motohiro 2011-04-14 15:22:12 -07:00 • committed by Linus Torvalds
parent fe936dfc23
commit 929bea7c71
1 changed files with 13 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

24
mm/vmscan.c
View file

@ -41,6 +41,7 @@
#include <linux/memcontrol.h>
#include <linux/delayacct.h>
#include <linux/sysctl.h>
#include <linux/oom.h>
#include <asm/tlbflush.h>
#include <asm/div64.h>
@ -1988,17 +1989,12 @@ static bool zone_reclaimable(struct zone *zone)
return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
}
/*
* 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.
*/
/* All zones in zonelist are unreclaimable? */
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) {
@ -2006,13 +2002,11 @@ static bool all_unreclaimable(struct zonelist *zonelist,
continue;
if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
continue;
if (zone_reclaimable(zone)) {
all_unreclaimable = false;
break;
}
if (!zone->all_unreclaimable)
return false;
}
return all_unreclaimable;
return true;
}
/*
@ -2108,6 +2102,14 @@ out:
if (sc->nr_reclaimed)
return sc->nr_reclaimed;
/*
* As hibernation is going on, kswapd is freezed so that it can't mark
* the zone into all_unreclaimable. Thus bypassing all_unreclaimable
* check.
*/
if (oom_killer_disabled)
return 0;
/* top priority shrink_zones still had more to do? don't OOM, then */
if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
return 1;