+
> +static long get_nr_evictable(struct lruvec *lruvec, unsigned long max_seq,
> + unsigned long *min_seq, bool can_swap, bool *need_aging)
> +{
> + int gen, type, zone;
> + long old = 0;
> + long young = 0;
> + long total = 0;
> + struct lru_gen_struct *lrugen = &lruvec->lrugen;
> +
> + for (type = !can_swap; type < ANON_AND_FILE; type++) {
> + unsigned long seq;
> +
> + for (seq = min_seq[type]; seq <= max_seq; seq++) {
> + long size = 0;
> +
> + gen = lru_gen_from_seq(seq);
> +
> + for (zone = 0; zone < MAX_NR_ZONES; zone++)
> + size += READ_ONCE(lrugen->nr_pages[gen][type][zone]);
> +
> + total += size;
> + if (seq == max_seq)
> + young += size;
> + if (seq + MIN_NR_GENS == max_seq)
> + old += size;
> + }
> + }
> +
> + /* try to spread pages out across MIN_NR_GENS+1 generations */
> + if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq)
> + *need_aging = true;
> + else if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS < max_seq)
> + *need_aging = false;
Can you explain/document the reason for the considering the below
conditions for ageing?
> + else if (young * MIN_NR_GENS > total)
> + *need_aging = true;
Are we trying to consdier the case of more than half the total pages
young as needing ageing? If so should MIN_NR_GENS be 2 instead of using
that #define? Or
> + else if (old * (MIN_NR_GENS + 2) < total)
> + *need_aging = true;
What is the significance of '+ 2' ?
> + else
> + *need_aging = false;
> +
> + return total > 0 ? total : 0;
> +}
> +
