On Wed, Dec 08, 2021 at 10:20:47PM -0800, Hugh Dickins wrote: > On Thu, 2 Dec 2021, Mel Gorman wrote: > ... > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > ... > > @@ -3478,14 +3520,18 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc) > > /* need some check for avoid more shrink_zone() */ > > } > > > > + if (!first_pgdat) > > + first_pgdat = zone->zone_pgdat; > > + > > /* See comment about same check for global reclaim above */ > > if (zone->zone_pgdat == last_pgdat) > > continue; > > last_pgdat = zone->zone_pgdat; > > shrink_node(zone->zone_pgdat, sc); > > - consider_reclaim_throttle(zone->zone_pgdat, sc); > > } > > > > + consider_reclaim_throttle(first_pgdat, sc); > > My tmpfs swapping load (tweaked to use huge pages more heavily than > in real life) is far from being a realistic load: but it was notably > slowed down by your throttling mods in 5.16-rc, and this patch makes > it well again - thanks. > > But: it very quickly hit NULL pointer until I changed that last line to > > if (first_pgdat) > consider_reclaim_throttle(first_pgdat, sc); > > I've given no thought as to whether that is the correct fix, > or if first_pgdat should be set earlier in the loop above. > It's the right fix, first_pgdat may be NULL if compaction can run for each zone in the zonelist which could be the case for a tmpfs swapping load that is huge page intensive. Thanks Hugh. -- Mel Gorman SUSE Labs
