Messages in this thread | | | Date | Fri, 15 Apr 2022 14:31:37 +0800 | Subject | Re: [PATCH v10 06/14] mm: multi-gen LRU: minimal implementation | From | Chen Wandun <> |
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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; else if (young * MIN_NR_GENS > total) *need_aging = true; else if (old * (MIN_NR_GENS + 2) < total) *need_aging = true; else *need_aging = false;
Thanks > .
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