Messages in this thread | | | Date | Fri, 15 Apr 2022 17:27:58 +0800 | Subject | Re: [PATCH v10 06/14] mm: multi-gen LRU: minimal implementation | From | Chen Wandun <> |
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在 2022/4/15 14:44, Yu Zhao 写道: > On Fri, Apr 15, 2022 at 02:31:37PM +0800, Chen Wandun wrote: >> >> 在 2022/4/15 13:25, Yu Zhao 写道: >>> On Fri, Apr 15, 2022 at 10:23:18AM +0800, Chen Wandun wrote: >>>> 在 2022/4/15 4:53, Yu Zhao 写道: >>>>> 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]. >>>> Can lrugen->lists[max_seq+1] also be non-empty for file LRU? >>> On reclaim path, no. But it can be forced to do so via debugfs. >>> >>>> such as in dont reclaim mapped file page case(isolation will fail). >>> You mean may_unmap=false? Pages stays in the same generation if >>> isolation fails. So lrugen->lists[min_seq] won't be empty in this >>> case. >>> >>>> If so, after aging, eviction will reclaim memory start from >>>> lrugen->lists[min_seq+1], but some oldest file page still >>>> remain in lrugen->lists[max_seq+1]. >>>> >>>> sort_folio can help to put misplaced pages to the right >>>> LRU list, but in this case, it does't help, because sort_folio >>>> only sort lrugen->lists[min_seq+1]. >>> On reclaim path, inc_max_seq() is only called when need_aging=true, >>> and this guarantees max_seq-min_seq[LRU_GEN_FILE]+1 < MAX_NR_GENS. >> yes, I think so, but I did't find the logical in function get_nr_evictable, >> or am I missing something >> >> 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; > This branch. > > And the following is also relavent: > > static int __init init_lru_gen(void) > { > BUILD_BUG_ON(MIN_NR_GENS + 1 >= MAX_NR_GENS); Got it, many thanks. Wandun > .
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