On Mon, Mar 21, 2022 at 6:52 AM Aneesh Kumar K.V
<aneesh.kumar@xxxxxxxxxxxxx> wrote:
>
> +
> > +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' ?
Will improve the comment according to my previous reply here [1].
[1] https://lore.kernel.org/linux-mm/CAOUHufYmUPZY0gCC+wYk6Vr1L8KEx+tJeEAhjpBfUnLJsAHq5A@xxxxxxxxxxxxxx/
