From 8008293888188c3923f5bd8a69370dae25ed14e5 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Fri, 31 Dec 2021 13:10:09 -0800 Subject: [PATCH] mm: vmscan: reduce throttling due to a failure to make progress -fix Hugh Dickins reported the following 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); The likely issue is that huge pages are a major component of the test workload. When this is the case, first_pgdat may never get set if compaction is ready to continue due to this check if (IS_ENABLED(CONFIG_COMPACTION) && sc->order > PAGE_ALLOC_COSTLY_ORDER && compaction_ready(zone, sc)) { sc->compaction_ready = true; continue; } If this was true for every zone in the zonelist, first_pgdat would never get set resulting in a NULL pointer exception. Link: https://lkml.kernel.org/r/20211209095453.GM3366@techsingularity.net Fixes: 1b4e3f26f9f75 ("mm: vmscan: Reduce throttling due to a failure to make progress") Signed-off-by: Mel Gorman Reported-by: Hugh Dickins Cc: Michal Hocko Cc: Vlastimil Babka Cc: Rik van Riel Cc: Mike Galbraith Cc: Darrick J. Wong Cc: Shakeel Butt Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/vmscan.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 4c4d5f6..700434d 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3530,7 +3530,8 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc) shrink_node(zone->zone_pgdat, sc); } - consider_reclaim_throttle(first_pgdat, sc); + if (first_pgdat) + consider_reclaim_throttle(first_pgdat, sc); /* * Restore to original mask to avoid the impact on the caller if we -- 2.7.4