commit ad2b8e601099a23dffffb53f91c18d874fe98854 upstream - WARNING: partial backport only Stable note: Not tracked in Bugzilla. This patch is very controversial for -stable. The upstream patch is addressing a completely different issue but accidentally contained an important fix. The workload in question was running memcached and then started IO in the background. memcached should stay resident but without this patch it gets swapped. Sometimes this manifests as a drop in throughput but mostly it was observed through /proc/vmstat. Commit [246e87a9: memcg: fix get_scan_count() for small targets] was meant to fix a problem whereby small scan targets on memcg were ignored causing priority to raise too sharply. It forced scanning to take place if the target was small, memcg or kswapd. >From the time it was introduced it cause excessive reclaim by kswapd with workloads being pushed to swap that previously would have stayed resident. This was accidentally fixed by commit [ad2b8e60: mm: memcg: remove optimization of keeping the root_mem_cgroup LRU lists empty] but that patchset is not suitable for backporting. The original patch came with no information on what workloads it benefits but the cost of it is obvious in that it forces scanning to take place on lists that would otherwise have been ignored such as small anonymous inactive lists. This patch partially reverts 246e87a9 so that small lists are not force scanned which means that IO-intensive workloads with small amounts of anonymous memory will not be swapped. Signed-off-by: Mel Gorman <mgorman@xxxxxxx> --- mm/vmscan.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index e5382ad..49d8547 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1849,9 +1849,6 @@ static void get_scan_count(struct zone *zone, struct scan_control *sc, bool force_scan = false; unsigned long nr_force_scan[2]; - /* kswapd does zone balancing and needs to scan this zone */ - if (scanning_global_lru(sc) && current_is_kswapd()) - force_scan = true; /* memcg may have small limit and need to avoid priority drop */ if (!scanning_global_lru(sc)) force_scan = true; -- 1.7.9.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>