Messages in this thread Patch in this message | | | From | KOSAKI Motohiro <> | Subject | [PATCH 1/5] vmscan: remove all_unreclaimable check from direct reclaim path completely | Date | Tue, 22 Mar 2011 20:05:55 +0900 (JST) |
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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 a zone 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 becase all_unreclaimable, it never return all_unreclaimable=0 beucase it typicall don't have reclaimable pages.
Eventually, oom-killer never works on such systems. Let's remove this problematic logic completely.
Reported-by: Andrey Vagin <avagin@openvz.org> Cc: Nick Piggin <npiggin@kernel.dk> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Rik van Riel <riel@redhat.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> --- 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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