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Commit bb21c7ce authored by KOSAKI Motohiro's avatar KOSAKI Motohiro Committed by Linus Torvalds
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vmscan: fix do_try_to_free_pages() return value when priority==0 reclaim failure 



Greg Thelen reported recent Johannes's stack diet patch makes kernel hang.
 His test is following.

  mount -t cgroup none /cgroups -o memory
  mkdir /cgroups/cg1
  echo $$ > /cgroups/cg1/tasks
  dd bs=1024 count=1024 if=/dev/null of=/data/foo
  echo $$ > /cgroups/tasks
  echo 1 > /cgroups/cg1/memory.force_empty

Actually, This OOM hard to try logic have been corrupted since following
two years old patch.

	commit a41f24ea
	Author: Nishanth Aravamudan <nacc@us.ibm.com>
	Date:   Tue Apr 29 00:58:25 2008 -0700

	    page allocator: smarter retry of costly-order allocations

Original intention was "return success if the system have shrinkable zones
though priority==0 reclaim was failure".  But the above patch changed to
"return nr_reclaimed if .....".  Oh, That forgot nr_reclaimed may be 0 if
priority==0 reclaim failure.

And Johannes's patch 0aeb2339 ("vmscan: remove all_unreclaimable scan
control") made it more corrupt.  Originally, priority==0 reclaim failure
on memcg return 0, but this patch changed to return 1.  It totally
confused memcg.

This patch fixes it completely.

Reported-by: default avatarGreg Thelen <gthelen@google.com>
Signed-off-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: default avatarGreg Thelen <gthelen@google.com>
Acked-by: default avatarBalbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 9e506f7a

mm/vmscan.c

+16 −13
Original line number Diff line number Diff line
@@ -1724,13 +1724,13 @@ 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 int shrink_zones(int priority, struct zonelist *zonelist,

static bool shrink_zones(int priority, struct zonelist *zonelist,

					struct scan_control *sc)

{

	enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);

	struct zoneref *z;

	struct zone *zone;

	int progress = 0;

	bool all_unreclaimable = true;



	for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,

					sc->nodemask) {
@@ -1757,9 +1757,9 @@ static int shrink_zones(int priority, struct zonelist *zonelist, 
		}



		shrink_zone(priority, zone, sc);

		progress = 1;

		all_unreclaimable = false;

	}

	return progress;

	return all_unreclaimable;

}



/*
@@ -1782,7 +1782,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 
					struct scan_control *sc)

{

	int priority;

	unsigned long ret = 0;

	bool all_unreclaimable;

	unsigned long total_scanned = 0;

	struct reclaim_state *reclaim_state = current->reclaim_state;

	unsigned long lru_pages = 0;
@@ -1813,7 +1813,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 
		sc->nr_scanned = 0;

		if (!priority)

			disable_swap_token();

		ret = shrink_zones(priority, zonelist, sc);

		all_unreclaimable = shrink_zones(priority, zonelist, sc);

		/*

		 * Don't shrink slabs when reclaiming memory from

		 * over limit cgroups
@@ -1826,10 +1826,8 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 
			}

		}

		total_scanned += sc->nr_scanned;

		if (sc->nr_reclaimed >= sc->nr_to_reclaim) {

			ret = sc->nr_reclaimed;

		if (sc->nr_reclaimed >= sc->nr_to_reclaim)

			goto out;

		}



		/*

		 * Try to write back as many pages as we just scanned.  This
@@ -1849,9 +1847,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 
		    priority < DEF_PRIORITY - 2)

			congestion_wait(BLK_RW_ASYNC, HZ/10);

	}

	/* top priority shrink_zones still had more to do? don't OOM, then */

	if (ret && scanning_global_lru(sc))

		ret = sc->nr_reclaimed;



out:

	/*

	 * Now that we've scanned all the zones at this priority level, note
@@ -1877,7 +1873,14 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 
	delayacct_freepages_end();

	put_mems_allowed();



	return ret;

	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)

		return 1;



	return 0;

}



unsigned long try_to_free_pages(struct zonelist *zonelist, int order,