Messages in this thread | | | Date | Thu, 10 Feb 2011 13:04:51 +0900 | Subject | Re: [patch] vmscan: fix zone shrinking exit when scan work is done | From | Minchan Kim <> |
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On Thu, Feb 10, 2011 at 12:46 AM, Johannes Weiner <hannes@cmpxchg.org> wrote: > Hi, > > I think this should fix the problem of processes getting stuck in > reclaim that has been reported several times. Kent actually > single-stepped through this code and noted that it was never exiting > shrink_zone(), which really narrowed it down a lot, considering the > tons of nested loops from the allocator down to the list shrinking. > > Hannes > > --- > From: Johannes Weiner <hannes@cmpxchg.org> > Subject: vmscan: fix zone shrinking exit when scan work is done > > '3e7d344 mm: vmscan: reclaim order-0 and use compaction instead of > lumpy reclaim' introduced an indefinite loop in shrink_zone(). > > It meant to break out of this loop when no pages had been reclaimed > and not a single page was even scanned. The way it would detect the > latter is by taking a snapshot of sc->nr_scanned at the beginning of > the function and comparing it against the new sc->nr_scanned after the > scan loop. But it would re-iterate without updating that snapshot, > looping forever if sc->nr_scanned changed at least once since > shrink_zone() was invoked. > > This is not the sole condition that would exit that loop, but it > requires other processes to change the zone state, as the reclaimer > that is stuck obviously can not anymore. > > This is only happening for higher-order allocations, where reclaim is > run back to back with compaction. > > Reported-by: Michal Hocko <mhocko@suse.cz> > Reported-by: Kent Overstreet <kent.overstreet@gmail.com> > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
-- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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