On Thu, Jun 14, 2012 at 04:13:12AM -0400, kosaki.motohiro@xxxxxxxxx wrote: > From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > Currently, do_try_to_free_pages() can enter livelock. Because of, > now vmscan has two conflicted policies. > > 1) kswapd sleep when it couldn't reclaim any page when reaching > priority 0. This is because to avoid kswapd() infinite > loop. That said, kswapd assume direct reclaim makes enough > free pages to use either regular page reclaim or oom-killer. > This logic makes kswapd -> direct-reclaim dependency. > 2) direct reclaim continue to reclaim without oom-killer until > kswapd turn on zone->all_unreclaimble. This is because > to avoid too early oom-kill. > This logic makes direct-reclaim -> kswapd dependency. > > In worst case, direct-reclaim may continue to page reclaim forever > when kswapd sleeps forever. > > We can't turn on zone->all_unreclaimable from direct reclaim path > because direct reclaim path don't take any lock and this way is racy. > > Thus this patch removes zone->all_unreclaimable field completely and > recalculates zone reclaimable state every time. > > Note: we can't take the idea that direct-reclaim see zone->pages_scanned > directly and kswapd continue to use zone->all_unreclaimable. Because, it > is racy. commit 929bea7c71 (vmscan: all_unreclaimable() use > zone->all_unreclaimable as a name) describes the detail. > > Reported-by: Aaditya Kumar <aaditya.kumar.30@xxxxxxxxx> > Reported-by: Ying Han <yinghan@xxxxxxxxxx> > Cc: Nick Piggin <npiggin@xxxxxxxxx> > Acked-by: Rik van Riel <riel@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Mel Gorman <mel@xxxxxxxxx> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > Cc: Minchan Kim <minchan.kim@xxxxxxxxx> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > @@ -2497,12 +2490,11 @@ loop_again: > shrink_zone(zone, &sc); > > reclaim_state->reclaimed_slab = 0; > - nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages); > + shrink_slab(&shrink, sc.nr_scanned, lru_pages); > sc.nr_reclaimed += reclaim_state->reclaimed_slab; > total_scanned += sc.nr_scanned; > > - if (nr_slab == 0 && !zone_reclaimable(zone)) > - zone->all_unreclaimable = 1; > + That IS a slight change in behaviour. But then, if you scanned 6 times the amount of reclaimable pages without freeing a single slab page, it's probably not worth going on. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>