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Message-ID: <CAGsJ_4wuy5Nhn0pdoz7YvzTXs9LCUrpxT5c4+Hd7-DGH3yBsog@mail.gmail.com>
Date: Tue, 10 Dec 2024 12:54:52 +0800
From: Barry Song <21cnbao@...il.com>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: akpm@...ux-foundation.org, mhocko@...e.com, hannes@...xchg.org,
yosryahmed@...gle.com, yuzhao@...gle.com, david@...hat.com,
willy@...radead.org, ryan.roberts@....com, wangkefeng.wang@...wei.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org, chenridong@...wei.com,
wangweiyang2@...wei.com, xieym_ict@...mail.com
Subject: Re: [PATCH v4 1/1] mm: vmascan: retry folios written back while
isolated for traditional LRU
On Mon, Dec 9, 2024 at 4:46 PM Chen Ridong <chenridong@...weicloud.com> wrote:
>
> From: Chen Ridong <chenridong@...wei.com>
>
> The commit 359a5e1416ca ("mm: multi-gen LRU: retry folios written back
> while isolated") only fixed the issue for mglru. However, this issue
> also exists in the traditional active/inactive LRU. This issue will be
> worse if THP is split, which makes the list longer and needs longer time
> to finish a batch of folios reclaim.
>
> This issue should be fixed in the same way for the traditional LRU.
> Therefore, the common logic was extracted to the 'find_folios_written_back'
> function firstly, which is then reused in the 'shrink_inactive_list'
> function. Finally, retry reclaiming those folios that may have missed the
> rotation for traditional LRU.
let's drop the cover-letter and refine the changelog.
>
> Signed-off-by: Chen Ridong <chenridong@...wei.com>
> ---
> include/linux/mmzone.h | 3 +-
> mm/vmscan.c | 108 +++++++++++++++++++++++++++++------------
> 2 files changed, 77 insertions(+), 34 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index b36124145a16..47c6e8c43dcd 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -391,6 +391,7 @@ struct page_vma_mapped_walk;
>
> #define LRU_GEN_MASK ((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF)
> #define LRU_REFS_MASK ((BIT(LRU_REFS_WIDTH) - 1) << LRU_REFS_PGOFF)
> +#define LRU_REFS_FLAGS (BIT(PG_referenced) | BIT(PG_workingset))
>
> #ifdef CONFIG_LRU_GEN
>
> @@ -406,8 +407,6 @@ enum {
> NR_LRU_GEN_CAPS
> };
>
> -#define LRU_REFS_FLAGS (BIT(PG_referenced) | BIT(PG_workingset))
> -
> #define MIN_LRU_BATCH BITS_PER_LONG
> #define MAX_LRU_BATCH (MIN_LRU_BATCH * 64)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 76378bc257e3..1f0d194f8b2f 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.
> @@ -1907,6 +1949,25 @@ static int current_may_throttle(void)
> return !(current->flags & PF_LOCAL_THROTTLE);
> }
>
> +static inline void acc_reclaimed_stat(struct reclaim_stat *stat,
> + struct reclaim_stat *curr)
> +{
> + int i;
> +
> + stat->nr_dirty += curr->nr_dirty;
> + stat->nr_unqueued_dirty += curr->nr_unqueued_dirty;
> + stat->nr_congested += curr->nr_congested;
> + stat->nr_writeback += curr->nr_writeback;
> + stat->nr_immediate += curr->nr_immediate;
> + stat->nr_pageout += curr->nr_pageout;
> + stat->nr_ref_keep += curr->nr_ref_keep;
> + stat->nr_unmap_fail += curr->nr_unmap_fail;
> + stat->nr_lazyfree_fail += curr->nr_lazyfree_fail;
> + stat->nr_demoted += curr->nr_demoted;
> + for (i = 0; i < ANON_AND_FILE; i++)
> + stat->nr_activate[i] = curr->nr_activate[i];
> +}
you had no this before, what's the purpose of this？
> +
> /*
> * shrink_inactive_list() is a helper for shrink_node(). It returns the number
> * of reclaimed pages
> @@ -1916,14 +1977,16 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
> enum lru_list lru)
> {
> LIST_HEAD(folio_list);
> + LIST_HEAD(clean_list);
> unsigned long nr_scanned;
> unsigned int nr_reclaimed = 0;
> unsigned long nr_taken;
> - struct reclaim_stat stat;
> + struct reclaim_stat stat, curr;
> bool file = is_file_lru(lru);
> enum vm_event_item item;
> struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> bool stalled = false;
> + bool skip_retry = false;
>
> while (unlikely(too_many_isolated(pgdat, file, sc))) {
> if (stalled)
> @@ -1957,10 +2020,20 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan,
> if (nr_taken == 0)
> return 0;
>
> - nr_reclaimed = shrink_folio_list(&folio_list, pgdat, sc, &stat, false);
> + memset(&stat, 0, sizeof(stat));
> +retry:
> + nr_reclaimed += shrink_folio_list(&folio_list, pgdat, sc, &curr, false);
> + find_folios_written_back(&folio_list, &clean_list, skip_retry);
> + acc_reclaimed_stat(&stat, &curr);
>
> spin_lock_irq(&lruvec->lru_lock);
> move_folios_to_lru(lruvec, &folio_list);
> + if (!list_empty(&clean_list)) {
> + list_splice_init(&clean_list, &folio_list);
> + skip_retry = true;
> + spin_unlock_irq(&lruvec->lru_lock);
> + goto retry;
> + }
>
> __mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(),
> stat.nr_demoted);
> @@ -4567,8 +4640,6 @@ 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 +4668,7 @@ 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
>
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