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

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
http://www.gossamer-threads.com/lists/linux/kernel/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>
hifive-unleashed-5.1
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
Show Stats 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;