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Date: Wed, 25 May 2022 19:43:15 +0800
From: Muchun Song <songmuchun@...edance.com>
To: Waiman Long <longman@...hat.com>
Cc: hannes@...xchg.org, mhocko@...nel.org, roman.gushchin@...ux.dev,
shakeelb@...gle.com, cgroups@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, duanxiongchun@...edance.com
Subject: Re: [PATCH v4 04/11] mm: vmscan: rework move_pages_to_lru()
On Tue, May 24, 2022 at 03:52:22PM -0400, Waiman Long wrote:
> 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@...edance.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().
>
Thanks. I'll replace them with local_lock/unlock_irq().
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