[PATCH v9 06/14] mm: multi-gen LRU: minimal implementation

[Barry Song]

> +static void inc_max_seq(struct lruvec *lruvec, unsigned long max_seq)
> +{
> +       int prev, next;
> +       int type, zone;
> +       struct lru_gen_struct *lrugen = &lruvec->lrugen;
> +
> +       spin_lock_irq(&lruvec->lru_lock);
> +
> +       VM_BUG_ON(!seq_is_valid(lruvec));
> +
> +       if (max_seq != lrugen->max_seq)
> +               goto unlock;
> +
> +       inc_min_seq(lruvec);
> +
> +       /* update the active/inactive LRU sizes for compatibility */
> +       prev = lru_gen_from_seq(lrugen->max_seq - 1);
> +       next = lru_gen_from_seq(lrugen->max_seq + 1);
> +
> +       for (type = 0; type < ANON_AND_FILE; type++) {
> +               for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> +                       enum lru_list lru = type * LRU_INACTIVE_FILE;
> +                       long delta = lrugen->nr_pages[prev][type][zone] -
> +                                    lrugen->nr_pages[next][type][zone];

this is confusing to me. does lrugen->nr_pages[next][type][zone] have a
chance to be none-zero even before max_seq is increased? some pages
can be in the next generation before the generation is born?

isn't it a bug if(lrugen->nr_pages[next][type][zone] > 0)? shouldn't it be？

delta = lrugen->nr_pages[prev][type][zone]；

> +
> +                       if (!delta)
> +                               continue;
> +
> +                       __update_lru_size(lruvec, lru, zone, delta);
> +                       __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, -delta);
> +               }
> +       }
> +
> +       for (type = 0; type < ANON_AND_FILE; type++)
> +               reset_ctrl_pos(lruvec, type, false);
> +
> +       /* make sure preceding modifications appear */
> +       smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1);
> +unlock:
> +       spin_unlock_irq(&lruvec->lru_lock);
> +}

Thanks
Barry