6.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: T.J. Mercier <tjmercier@xxxxxxxxxx>
commit 6867c7a3320669cbe44b905a3eb35db725c6d470 upstream.
When a memcg is in the process of being released mem_cgroup_tryget will
fail because its reference count has already reached 0. This can happen
during reclaim if the memcg has already been offlined, and we reclaim all
remaining pages attributed to the offlined memcg. shrink_many attempts to
skip the empty memcg in this case, and continue reclaiming from the
remaining memcgs in the old generation. If there is only one memcg
remaining, or if all remaining memcgs are in the process of being released
then shrink_many will spin until all memcgs have finished being released.
The release occurs through a workqueue, so it can take a while before
kswapd is able to make any further progress.
This fix results in reductions in kswapd activity and direct reclaim in
a test where 28 apps (working set size > total memory) are repeatedly
launched in a random sequence:
A B delta ratio(%)
allocstall_movable 5962 3539 -2423 -40.64
allocstall_normal 2661 2417 -244 -9.17
kswapd_high_wmark_hit_quickly 53152 7594 -45558 -85.71
pageoutrun 57365 11750 -45615 -79.52
Link: https://lkml.kernel.org/r/20230814151636.1639123-1-tjmercier@xxxxxxxxxx
Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists")
Signed-off-by: T.J. Mercier <tjmercier@xxxxxxxxxx>
Acked-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/vmscan.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4818,16 +4818,17 @@ void lru_gen_release_memcg(struct mem_cg
spin_lock_irq(&pgdat->memcg_lru.lock);
- VM_WARN_ON_ONCE(hlist_nulls_unhashed(&lruvec->lrugen.list));
+ if (hlist_nulls_unhashed(&lruvec->lrugen.list))
+ goto unlock;
gen = lruvec->lrugen.gen;
- hlist_nulls_del_rcu(&lruvec->lrugen.list);
+ hlist_nulls_del_init_rcu(&lruvec->lrugen.list);
pgdat->memcg_lru.nr_memcgs[gen]--;
if (!pgdat->memcg_lru.nr_memcgs[gen] && gen == get_memcg_gen(pgdat->memcg_lru.seq))
WRITE_ONCE(pgdat->memcg_lru.seq, pgdat->memcg_lru.seq + 1);
-
+unlock:
spin_unlock_irq(&pgdat->memcg_lru.lock);
}
}
@@ -5398,8 +5399,10 @@ restart:
rcu_read_lock();
hlist_nulls_for_each_entry_rcu(lrugen, pos, &pgdat->memcg_lru.fifo[gen][bin], list) {
- if (op)
+ if (op) {
lru_gen_rotate_memcg(lruvec, op);
+ op = 0;
+ }
mem_cgroup_put(memcg);
@@ -5407,7 +5410,7 @@ restart:
memcg = lruvec_memcg(lruvec);
if (!mem_cgroup_tryget(memcg)) {
- op = 0;
+ lru_gen_release_memcg(memcg);
memcg = NULL;
continue;
}
