Messages in this thread | | | Date | Thu, 14 Apr 2022 14:53:34 -0600 | From | Yu Zhao <> | Subject | Re: [PATCH v10 06/14] mm: multi-gen LRU: minimal implementation |
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On Thu, Apr 14, 2022 at 07:47:54PM +0800, Chen Wandun wrote: > > On 2022/4/7 11:15, Yu Zhao wrote: > > +static void inc_min_seq(struct lruvec *lruvec) > > +{ > > + int type; > > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > > + > > + VM_BUG_ON(!seq_is_valid(lruvec)); > > + > > + for (type = 0; type < ANON_AND_FILE; type++) { > > + if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > > + continue; > I'm confused about relation between aging and LRU list operation. > > In function inc_max_seq, both min_seq and max_seq will increase, > the lrugen->lists[] indexed by lru_gen_from_seq(max_seq + 1) may > be non-empty?
Yes.
> for example, > before inc_max_seq: > min_seq == 0, lrugen->lists[0][type][zone] > max_seq ==3, lrugen->lists[3][type][zone] > > after inc_max_seq: > min_seq ==1, lrugen->lists[1][type][zone] > max_seq ==4, lrugen->lists[0][type][zone] > > If lrugen->lists[0][type][zone] is not empty before inc_max_seq and it is > the most inactive list,however lurgen->lists[0][type][zone] will become > the most active list after inc_max_seq.
Correct.
> So, in this place, > > if (get_nr_gens(lruvec, type) != MAX_NR_GENS) > continue; > > should change to > > if (get_nr_gens(lruvec, type) == MAX_NR_GENS) > continue;
No, because max/min_seq will overlap if we do so.
lrugen->lists[max_seq+1] can only be non-empty for anon LRU, for a couple of reasons: 1. We can't swap at all. 2. Swapping is constrained, e.g., swapfile is full.
Both cases are similar to a producer (the aging) overrunning a consumer (the eviction). We used to handle them, but I simplified the code because I don't feel they are worth handling [1].
[1] https://lore.kernel.org/r/CAOUHufbDfwgm8PgCGkhCjbhMbm=fekfjgRR56NL-j+5iUGfVuw@mail.gmail.com/
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