From: Kairui Song Right now, if eviction triggers aging, the reclaimer will abort. This is not the optimal strategy for several reasons. Aborting the reclaim early wastes a reclaim cycle when under pressure, and for concurrent reclaim, if the LRU is under aging, all concurrent reclaimers might fail. And if the age has just finished, new cold folios exposed by the aging are not reclaimed until the next reclaim iteration. What's more, the current aging trigger is quite lenient, having 3 gens with a reclaim priority lower than default will trigger aging, and blocks reclaiming from one memcg. This wastes reclaim retry cycles easily. And in the worst case, if the reclaim is making slower progress and all following attempts fail due to being blocked by aging, it triggers unexpected early OOM. And if a lruvec requires aging, it doesn't mean it's hot. Instead, the lruvec could be idle for quite a while, and hence it might contain lots of cold folios to be reclaimed. While it's helpful to rotate memcg LRU after aging for global reclaim, as global reclaim fairness is coupled with the rotation in shrink_many, memcg fairness is instead handled by cgroup iteration in shrink_node_memcgs. So, for memcg level pressure, this abort is not the key part for keeping the fairness. And in most cases, there is no need to age, and fairness must be achieved by upper-level reclaim control. So instead, just keep the scanning going unless one whole batch of folios failed to be isolated or enough folios have been scanned, which is triggered by evict_folios returning 0. And only abort for global reclaim after one batch, so when there are fewer memcgs, progress is still made, and the fairness mechanism described above still works fine. And in most cases, the one more batch attempt for global reclaim might just be enough to satisfy what the reclaimer needs, hence improving global reclaim performance by reducing reclaim retry cycles. Rotation is still there after the reclaim is done, which still follows the comment in mmzone.h. And fairness still looking good. Signed-off-by: Kairui Song --- mm/vmscan.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 9c28afb0219c..b3371877762a 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4987,7 +4987,7 @@ static bool should_abort_scan(struct lruvec *lruvec, struct scan_control *sc) */ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) { - bool need_rotate = false; + bool need_rotate = false, should_age = false; long nr_batch, nr_to_scan; int swappiness = get_swappiness(lruvec, sc); struct mem_cgroup *memcg = lruvec_memcg(lruvec); @@ -5005,7 +5005,7 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) if (should_run_aging(lruvec, max_seq, sc, swappiness)) { if (try_to_inc_max_seq(lruvec, max_seq, swappiness, false)) need_rotate = true; - break; + should_age = true; } nr_batch = min(nr_to_scan, MIN_LRU_BATCH); @@ -5016,6 +5016,10 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) if (should_abort_scan(lruvec, sc)) break; + /* For cgroup reclaim, fairness is handled by iterator, not rotation */ + if (root_reclaim(sc) && should_age) + break; + nr_to_scan -= delta; cond_resched(); } -- 2.53.0