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SubjectRe: [PATCH v4 04/11] mm: vmscan: rework move_pages_to_lru()
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On 5/24/22 02:05, Muchun Song wrote:
> In the later patch, we will reparent the LRU pages. The pages moved to
> appropriate LRU list can be reparented during the process of the
> move_pages_to_lru(). So holding a lruvec lock by the caller is wrong, we
> should use the more general interface of folio_lruvec_relock_irq() to
> acquire the correct lruvec lock.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> mm/vmscan.c | 49 +++++++++++++++++++++++++------------------------
> 1 file changed, 25 insertions(+), 24 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 1678802e03e7..761d5e0dd78d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2230,23 +2230,28 @@ static int too_many_isolated(struct pglist_data *pgdat, int file,
> * move_pages_to_lru() moves pages from private @list to appropriate LRU list.
> * On return, @list is reused as a list of pages to be freed by the caller.
> *
> - * Returns the number of pages moved to the given lruvec.
> + * Returns the number of pages moved to the appropriate LRU list.
> + *
> + * Note: The caller must not hold any lruvec lock.
> */
> -static unsigned int move_pages_to_lru(struct lruvec *lruvec,
> - struct list_head *list)
> +static unsigned int move_pages_to_lru(struct list_head *list)
> {
> - int nr_pages, nr_moved = 0;
> + int nr_moved = 0;
> + struct lruvec *lruvec = NULL;
> LIST_HEAD(pages_to_free);
> - struct page *page;
>
> while (!list_empty(list)) {
> - page = lru_to_page(list);
> + int nr_pages;
> + struct folio *folio = lru_to_folio(list);
> + struct page *page = &folio->page;
> +
> + lruvec = folio_lruvec_relock_irq(folio, lruvec);
> VM_BUG_ON_PAGE(PageLRU(page), page);
> list_del(&page->lru);
> if (unlikely(!page_evictable(page))) {
> - spin_unlock_irq(&lruvec->lru_lock);
> + unlock_page_lruvec_irq(lruvec);
> putback_lru_page(page);
> - spin_lock_irq(&lruvec->lru_lock);
> + lruvec = NULL;
> continue;
> }
>
> @@ -2267,20 +2272,16 @@ static unsigned int move_pages_to_lru(struct lruvec *lruvec,
> __clear_page_lru_flags(page);
>
> if (unlikely(PageCompound(page))) {
> - spin_unlock_irq(&lruvec->lru_lock);
> + unlock_page_lruvec_irq(lruvec);
> destroy_compound_page(page);
> - spin_lock_irq(&lruvec->lru_lock);
> + lruvec = NULL;
> } else
> list_add(&page->lru, &pages_to_free);
>
> continue;
> }
>
> - /*
> - * All pages were isolated from the same lruvec (and isolation
> - * inhibits memcg migration).
> - */
> - VM_BUG_ON_PAGE(!folio_matches_lruvec(page_folio(page), lruvec), page);
> + VM_BUG_ON_PAGE(!folio_matches_lruvec(folio, lruvec), page);
> add_page_to_lru_list(page, lruvec);
> nr_pages = thp_nr_pages(page);
> nr_moved += nr_pages;
> @@ -2288,6 +2289,8 @@ static unsigned int move_pages_to_lru(struct lruvec *lruvec,
> workingset_age_nonresident(lruvec, nr_pages);
> }
>
> + if (lruvec)
> + unlock_page_lruvec_irq(lruvec);
> /*
> * To save our caller's stack, now use input list for pages to free.
> */
> @@ -2359,16 +2362,16 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
>
> nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, &stat, false);
>
> - spin_lock_irq(&lruvec->lru_lock);
> - move_pages_to_lru(lruvec, &page_list);
> + move_pages_to_lru(&page_list);
>
> + local_irq_disable();
> __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
> item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
> if (!cgroup_reclaim(sc))
> __count_vm_events(item, nr_reclaimed);
> __count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
> __count_vm_events(PGSTEAL_ANON + file, nr_reclaimed);
> - spin_unlock_irq(&lruvec->lru_lock);
> + local_irq_enable();
>
> lru_note_cost(lruvec, file, stat.nr_pageout);
> mem_cgroup_uncharge_list(&page_list);
> @@ -2498,18 +2501,16 @@ static void shrink_active_list(unsigned long nr_to_scan,
> /*
> * Move pages back to the lru list.
> */
> - spin_lock_irq(&lruvec->lru_lock);
> -
> - nr_activate = move_pages_to_lru(lruvec, &l_active);
> - nr_deactivate = move_pages_to_lru(lruvec, &l_inactive);
> + nr_activate = move_pages_to_lru(&l_active);
> + nr_deactivate = move_pages_to_lru(&l_inactive);
> /* Keep all free pages in l_active list */
> list_splice(&l_inactive, &l_active);
>
> + local_irq_disable();
> __count_vm_events(PGDEACTIVATE, nr_deactivate);
> __count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate);
> -
> __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
> - spin_unlock_irq(&lruvec->lru_lock);
> + local_irq_enable();
>
> mem_cgroup_uncharge_list(&l_active);
> free_unref_page_list(&l_active);

Note that the RT engineers will likely change the
local_irq_disable()/local_irq_enable() to
local_lock_irq()/local_unlock_irq().

Cheers,
Longman

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