inc_max_seq() will try to inc_min_seq() if nr_gens == MAX_NR_GENS. This is because the generations are reused (the last oldest now empty generation will become the next youngest generation).
inc_min_seq() is retried until successful, dropping the lru_lock and yielding the CPU on each failure, and retaking the lock before trying again:
while (!inc_min_seq(lruvec, type, can_swap)) { spin_unlock_irq(&lruvec->lru_lock); cond_resched(); spin_lock_irq(&lruvec->lru_lock); }
However, the initial condition that required incrementing the min_seq (nr_gens == MAX_NR_GENS) is not retested. This can change by another call to inc_max_seq() from run_aging() with force_scan=true from the debugfs interface.
Since the eviction stalls when the nr_gens == MIN_NR_GENS, avoid unnecessarily incrementing the min_seq by rechecking the number of generations before each attempt.
This issue was uncovered in previous discussion on the list by Yu Zhao and Aneesh Kumar [1].
[1] https://lore.kernel.org/linux-mm/CAOUHufbO7CaVm=xjEb1avDhHVvnC8pJmGyKcFf2iY_...
Fixes: d6c3af7d8a2b ("mm: multi-gen LRU: debugfs interface") Cc: stable@vger.kernel.org Cc: Yu Zhao yuzhao@google.com Cc: Aneesh Kumar K V aneesh.kumar@linux.ibm.com Cc: Andrew Morton akpm@linux-foundation.org Signed-off-by: Kalesh Singh kaleshsingh@google.com ---
Changes in v2: - Add Fixes tag and cc stable
mm/vmscan.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c index 489a4fc7d9b1..6eecd291756c 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4439,7 +4439,7 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan) int prev, next; int type, zone; struct lru_gen_folio *lrugen = &lruvec->lrugen; - +restart: spin_lock_irq(&lruvec->lru_lock);
VM_WARN_ON_ONCE(!seq_is_valid(lruvec)); @@ -4450,11 +4450,12 @@ static void inc_max_seq(struct lruvec *lruvec, bool can_swap, bool force_scan)
VM_WARN_ON_ONCE(!force_scan && (type == LRU_GEN_FILE || can_swap));
- while (!inc_min_seq(lruvec, type, can_swap)) { - spin_unlock_irq(&lruvec->lru_lock); - cond_resched(); - spin_lock_irq(&lruvec->lru_lock); - } + if (inc_min_seq(lruvec, type, can_swap)) + continue; + + spin_unlock_irq(&lruvec->lru_lock); + cond_resched(); + goto restart; }
/*