Messages in this thread Patch in this message | | | Date | Thu, 9 Dec 2021 09:54:53 +0000 | From | Mel Gorman <> | Subject | [PATCH] mm: vmscan: reduce throttling due to a failure to make progress -fix |
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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.
This is a fix to the mmotm patch mm-vmscan-reduce-throttling-due-to-a-failure-to-make-progress.patch
Reported-by: Hugh Dickins <hughd@google.com> Signed-off-by: Mel Gorman <mgorman@techsingularity.net> --- mm/vmscan.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c index 4c4d5f6cd8a3..700434db5735 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
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