Re: [RFC PATCH v3 1/2] mm: vmascan: add find_folios_written_back() helper

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

On Wed, Dec 4, 2024 at 5:11 PM Chen Ridong <chenridong@huaweicloud.com> wrote:
>
> From: Chen Ridong <chenridong@huawei.com>
>
> Add find_folios_written_back() helper, which will be called in the
> shrink_inactive_list function in subsequent patch.

This is not about adding a helper but rather extracting a function
that can be used
by both lru_gen and the traditional active/inactive LRU. Making it a
separate patch
may not be ideal, as it isn’t an external function that warrants
special attention.
Combining patch 1 and patch 2 into a single patch creates a more cohesive and
logical flow, making it easier to review.

>
> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> ---
>  mm/vmscan.c | 73 +++++++++++++++++++++++++++++++----------------------
>  1 file changed, 43 insertions(+), 30 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 76378bc257e3..af1ff76f83e7 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -283,6 +283,48 @@ static void set_task_reclaim_state(struct task_struct *task,
>         task->reclaim_state = rs;
>  }
>
> +/**
> + * find_folios_written_back - Find and move the written back folios to a new list.
> + * @list: filios list
> + * @clean: the written back folios list
> + * @skip: whether skip to move the written back folios to clean list.
> + */
> +static inline void find_folios_written_back(struct list_head *list,
> +               struct list_head *clean, bool skip)
> +{
> +       struct folio *folio;
> +       struct folio *next;
> +
> +       list_for_each_entry_safe_reverse(folio, next, list, lru) {
> +               if (!folio_evictable(folio)) {
> +                       list_del(&folio->lru);
> +                       folio_putback_lru(folio);
> +                       continue;
> +               }
> +
> +               if (folio_test_reclaim(folio) &&
> +                   (folio_test_dirty(folio) || folio_test_writeback(folio))) {
> +                       /* restore LRU_REFS_FLAGS cleared by isolate_folio() */
> +                       if (lru_gen_enabled() && folio_test_workingset(folio))
> +                               folio_set_referenced(folio);
> +                       continue;
> +               }
> +
> +               if (skip || folio_test_active(folio) || folio_test_referenced(folio) ||
> +                   folio_mapped(folio) || folio_test_locked(folio) ||
> +                   folio_test_dirty(folio) || folio_test_writeback(folio)) {
> +                       /* don't add rejected folios to the oldest generation */
> +                       if (lru_gen_enabled())
> +                               set_mask_bits(&folio->flags, LRU_REFS_MASK | LRU_REFS_FLAGS,
> +                                             BIT(PG_active));
> +                       continue;
> +               }
> +
> +               /* retry folios that may have missed folio_rotate_reclaimable() */
> +               list_move(&folio->lru, clean);
> +       }
> +}
> +
>  /*
>   * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to
>   * scan_control->nr_reclaimed.
> @@ -4567,8 +4609,6 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap
>         int reclaimed;
>         LIST_HEAD(list);
>         LIST_HEAD(clean);
> -       struct folio *folio;
> -       struct folio *next;
>         enum vm_event_item item;
>         struct reclaim_stat stat;
>         struct lru_gen_mm_walk *walk;
> @@ -4597,34 +4637,7 @@ static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swap
>                         scanned, reclaimed, &stat, sc->priority,
>                         type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON);
>
> -       list_for_each_entry_safe_reverse(folio, next, &list, lru) {
> -               if (!folio_evictable(folio)) {
> -                       list_del(&folio->lru);
> -                       folio_putback_lru(folio);
> -                       continue;
> -               }
> -
> -               if (folio_test_reclaim(folio) &&
> -                   (folio_test_dirty(folio) || folio_test_writeback(folio))) {
> -                       /* restore LRU_REFS_FLAGS cleared by isolate_folio() */
> -                       if (folio_test_workingset(folio))
> -                               folio_set_referenced(folio);
> -                       continue;
> -               }
> -
> -               if (skip_retry || folio_test_active(folio) || folio_test_referenced(folio) ||
> -                   folio_mapped(folio) || folio_test_locked(folio) ||
> -                   folio_test_dirty(folio) || folio_test_writeback(folio)) {
> -                       /* don't add rejected folios to the oldest generation */
> -                       set_mask_bits(&folio->flags, LRU_REFS_MASK | LRU_REFS_FLAGS,
> -                                     BIT(PG_active));
> -                       continue;
> -               }
> -
> -               /* retry folios that may have missed folio_rotate_reclaimable() */
> -               list_move(&folio->lru, &clean);
> -       }
> -
> +       find_folios_written_back(&list, &clean, skip_retry);
>         spin_lock_irq(&lruvec->lru_lock);
>
>         move_folios_to_lru(lruvec, &list);
> --
> 2.34.1
>

Thanks
Barry