RE: [PATCH RFC] mm: mglru: provide a separate list for lazyfree anon folios

[Barry Song <21cnbao@gmail.com>]

>> +++ b/include/linux/mmzone.h
>> @@ -434,7 +434,7 @@ struct lru_gen_folio {
>>  	/* the birth time of each generation in jiffies */
>>  	unsigned long timestamps[MAX_NR_GENS];
>>  	/* the multi-gen LRU lists, lazily sorted on eviction */
>> -	struct list_head
>> folios[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
>> +	struct list_head folios[MAX_NR_GENS][ANON_AND_FILE +
>> 1][MAX_NR_ZONES];
> This also divides lazy free filio into MAX_NR_ZONES generations.
> The gen of a lazy free filio depends on the gen in the anno list before
> it is marked as lazy free. Whether it will happen that lazy free filios
> are released in an order that is not consistent with the order of the mark?

No, this separate list ensures that lazyfree folios are released in the
same order they were marked as lazyfree. Note that any newly marked
lazyfree folio is always placed in the most likely reclaimed
generation, regardless of the list.

static void lru_lazyfree(struct lruvec *lruvec, struct folio *folio)
{
        long nr_pages = folio_nr_pages(folio);

        if (!folio_test_anon(folio) || !folio_test_swapbacked(folio) ||
            folio_test_swapcache(folio) || folio_test_unevictable(folio))
                return;

        lruvec_del_folio(lruvec, folio);
        folio_clear_active(folio);
        folio_clear_referenced(folio);
        /*
         * Lazyfree folios are clean anonymous folios.  They have
         * the swapbacked flag cleared, to distinguish them from normal
         * anonymous folios
         */
        folio_clear_swapbacked(folio);
        lruvec_add_folio(lruvec, folio);

        __count_vm_events(PGLAZYFREE, nr_pages);
        __count_memcg_events(lruvec_memcg(lruvec), PGLAZYFREE, nr_pages);
}

Thanks
Barry