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SubjectRe: [resend][PATCH] mm, vmscan: fix do_try_to_free_pages() livelock
On Thu, Jun 14, 2012 at 04:13:12AM -0400, kosaki.motohiro@gmail.com wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>
> 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@gmail.com>
> Reported-by: Ying Han <yinghan@google.com>
> Cc: Nick Piggin <npiggin@gmail.com>
> Acked-by: Rik van Riel <riel@redhat.com>
> Cc: Michal Hocko <mhocko@suse.cz>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Minchan Kim <minchan.kim@gmail.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

> @@ -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.


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