shrink_one() can return immediately for empty or protected memcgs, and try_to_shrink_lruvec() can break out before reaching its cond_resched(). A scan through many memcgs can repeatedly rotate entries without giving other runnable tasks a scheduling opportunity.
Call cond_resched_tasks_rcu_qs() (as the existing shrink_lruvec() loop does) after shrink_one(), while the memcg reference still pins the cursor and before reacquiring the RCU read lock. Also call it between bins and nulls-marker retries, covering scans that skip every entry. Signed-off-by: Max Kellermann <[email protected]> --- mm/vmscan.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/mm/vmscan.c b/mm/vmscan.c index 922c59eb9629..c9d53546dc10 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5194,6 +5194,9 @@ static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc) gen = get_memcg_gen(READ_ONCE(pgdat->memcg_lru.seq)); bin = first_bin = get_random_u32_below(MEMCG_NR_BINS); restart: + /* Yield between bins/retries that contain only skipped entries. */ + cond_resched_tasks_rcu_qs(); + op = 0; memcg = NULL; @@ -5224,6 +5227,14 @@ static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc) op = shrink_one(lruvec, sc); + /* + * Empty or protected memcgs can bypass the + * rescheduling points in page reclaim. The memcg + * reference pins our cursor while we yield outside + * the RCU read-side critical section. + */ + cond_resched_tasks_rcu_qs(); + rcu_read_lock(); if (should_abort_scan(lruvec, sc)) -- 2.47.3
