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Date: Tue, 21 Jun 2022 20:56:58 +0800
From: Muchun Song <songmuchun@...edance.com>
To: akpm@...ux-foundation.org, hannes@...xchg.org, longman@...hat.com,
mhocko@...nel.org, roman.gushchin@...ux.dev, shakeelb@...gle.com
Cc: cgroups@...r.kernel.org, duanxiongchun@...edance.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Muchun Song <songmuchun@...edance.com>
Subject: [PATCH v6 11/11] mm: lru: use lruvec lock to serialize memcg changes
As described by commit fc574c23558c ("mm/swap.c: serialize memcg
changes in pagevec_lru_move_fn"), TestClearPageLRU() aims to
serialize mem_cgroup_move_account() during pagevec_lru_move_fn().
Now folio_lruvec_lock*() has the ability to detect whether page
memcg has been changed. So we can use lruvec lock to serialize
mem_cgroup_move_account() during pagevec_lru_move_fn(). This
change is a partial revert of the commit fc574c23558c ("mm/swap.c:
serialize memcg changes in pagevec_lru_move_fn").
And pagevec_lru_move_fn() is more hot compare with
mem_cgroup_move_account(), removing an atomic operation would be
an optimization. Also this change would not dirty cacheline for a
page which isn't on the LRU.
Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
mm/memcontrol.c | 34 ++++++++++++++++++++++++++++++++++
mm/swap.c | 32 +++++++++++++++-----------------
mm/vmscan.c | 16 +++++++---------
3 files changed, 56 insertions(+), 26 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 803dbdf5f233..85adc43c5a25 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1330,10 +1330,39 @@ struct lruvec *folio_lruvec_lock(struct folio *folio)
lruvec = folio_lruvec(folio);
spin_lock(&lruvec->lru_lock);
+ /*
+ * The memcg of the page can be changed by any the following routines:
+ *
+ * 1) mem_cgroup_move_account() or
+ * 2) memcg_reparent_objcgs()
+ *
+ * The possible bad scenario would like:
+ *
+ * CPU0: CPU1: CPU2:
+ * lruvec = folio_lruvec()
+ *
+ * if (!isolate_lru_page())
+ * mem_cgroup_move_account()
+ *
+ * memcg_reparent_objcgs()
+ *
+ * spin_lock(&lruvec->lru_lock)
+ * ^^^^^^
+ * wrong lock
+ *
+ * Either CPU1 or CPU2 can change page memcg, so we need to check
+ * whether page memcg is changed, if so, we should reacquire the
+ * new lruvec lock.
+ */
if (unlikely(lruvec_memcg(lruvec) != folio_memcg(folio))) {
spin_unlock(&lruvec->lru_lock);
goto retry;
}
+
+ /*
+ * When we reach here, it means that the folio_memcg(folio) is
+ * stable.
+ */
rcu_read_unlock();
return lruvec;
@@ -1361,6 +1390,7 @@ struct lruvec *folio_lruvec_lock_irq(struct folio *folio)
lruvec = folio_lruvec(folio);
spin_lock_irq(&lruvec->lru_lock);
+ /* See the comments in folio_lruvec_lock(). */
if (unlikely(lruvec_memcg(lruvec) != folio_memcg(folio))) {
spin_unlock_irq(&lruvec->lru_lock);
goto retry;
@@ -1394,6 +1424,7 @@ struct lruvec *folio_lruvec_lock_irqsave(struct folio *folio,
lruvec = folio_lruvec(folio);
spin_lock_irqsave(&lruvec->lru_lock, *flags);
+ /* See the comments in folio_lruvec_lock(). */
if (unlikely(lruvec_memcg(lruvec) != folio_memcg(folio))) {
spin_unlock_irqrestore(&lruvec->lru_lock, *flags);
goto retry;
@@ -5809,7 +5840,10 @@ static int mem_cgroup_move_account(struct page *page,
obj_cgroup_put(rcu_dereference(from->objcg));
rcu_read_unlock();
+ /* See the comments in folio_lruvec_lock(). */
+ spin_lock(&from_vec->lru_lock);
folio->memcg_data = (unsigned long)rcu_access_pointer(to->objcg);
+ spin_unlock(&from_vec->lru_lock);
__folio_memcg_unlock(from);
diff --git a/mm/swap.c b/mm/swap.c
index 987dcbd93ffa..0fc59409e27d 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -196,6 +196,7 @@ static void lru_add_fn(struct lruvec *lruvec, struct folio *folio)
VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
+ folio_set_lru(folio);
/*
* Is an smp_mb__after_atomic() still required here, before
* folio_evictable() tests the mlocked flag, to rule out the possibility
@@ -238,14 +239,8 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn)
for (i = 0; i < folio_batch_count(fbatch); i++) {
struct folio *folio = fbatch->folios[i];
- /* block memcg migration while the folio moves between lru */
- if (move_fn != lru_add_fn && !folio_test_clear_lru(folio))
- continue;
-
lruvec = folio_lruvec_relock_irqsave(folio, lruvec, &flags);
move_fn(lruvec, folio);
-
- folio_set_lru(folio);
}
if (lruvec)
@@ -265,7 +260,7 @@ static void folio_batch_add_and_move(struct folio_batch *fbatch,
static void lru_move_tail_fn(struct lruvec *lruvec, struct folio *folio)
{
- if (!folio_test_unevictable(folio)) {
+ if (folio_test_lru(folio) && !folio_test_unevictable(folio)) {
lruvec_del_folio(lruvec, folio);
folio_clear_active(folio);
lruvec_add_folio_tail(lruvec, folio);
@@ -348,7 +343,8 @@ void lru_note_cost_folio(struct folio *folio)
static void folio_activate_fn(struct lruvec *lruvec, struct folio *folio)
{
- if (!folio_test_active(folio) && !folio_test_unevictable(folio)) {
+ if (folio_test_lru(folio) && !folio_test_active(folio) &&
+ !folio_test_unevictable(folio)) {
long nr_pages = folio_nr_pages(folio);
lruvec_del_folio(lruvec, folio);
@@ -394,12 +390,9 @@ static void folio_activate(struct folio *folio)
{
struct lruvec *lruvec;
- if (folio_test_clear_lru(folio)) {
- lruvec = folio_lruvec_lock_irq(folio);
- folio_activate_fn(lruvec, folio);
- lruvec_unlock_irq(lruvec);
- folio_set_lru(folio);
- }
+ lruvec = folio_lruvec_lock_irq(folio);
+ folio_activate_fn(lruvec, folio);
+ lruvec_unlock_irq(lruvec);
}
#endif
@@ -542,6 +535,9 @@ static void lru_deactivate_file_fn(struct lruvec *lruvec, struct folio *folio)
bool active = folio_test_active(folio);
long nr_pages = folio_nr_pages(folio);
+ if (!folio_test_lru(folio))
+ return;
+
if (folio_test_unevictable(folio))
return;
@@ -580,7 +576,8 @@ static void lru_deactivate_file_fn(struct lruvec *lruvec, struct folio *folio)
static void lru_deactivate_fn(struct lruvec *lruvec, struct folio *folio)
{
- if (folio_test_active(folio) && !folio_test_unevictable(folio)) {
+ if (folio_test_lru(folio) && folio_test_active(folio) &&
+ !folio_test_unevictable(folio)) {
long nr_pages = folio_nr_pages(folio);
lruvec_del_folio(lruvec, folio);
@@ -596,8 +593,9 @@ static void lru_deactivate_fn(struct lruvec *lruvec, struct folio *folio)
static void lru_lazyfree_fn(struct lruvec *lruvec, struct folio *folio)
{
- if (folio_test_anon(folio) && folio_test_swapbacked(folio) &&
- !folio_test_swapcache(folio) && !folio_test_unevictable(folio)) {
+ if (folio_test_lru(folio) && folio_test_anon(folio) &&
+ folio_test_swapbacked(folio) && !folio_test_swapcache(folio) &&
+ !folio_test_unevictable(folio)) {
long nr_pages = folio_nr_pages(folio);
lruvec_del_folio(lruvec, folio);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 51b1607c81e4..11e1f6fc5898 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4864,21 +4864,19 @@ void check_move_unevictable_pages(struct pagevec *pvec)
if (PageTransTail(page))
continue;
- nr_pages = thp_nr_pages(page);
+ nr_pages = folio_nr_pages(folio);
pgscanned += nr_pages;
- /* block memcg migration during page moving between lru */
- if (!TestClearPageLRU(page))
+ lruvec = folio_lruvec_relock_irq(folio, lruvec);
+ if (!folio_test_lru(folio) || !folio_test_unevictable(folio))
continue;
- lruvec = folio_lruvec_relock_irq(folio, lruvec);
- if (page_evictable(page) && PageUnevictable(page)) {
- del_page_from_lru_list(page, lruvec);
- ClearPageUnevictable(page);
- add_page_to_lru_list(page, lruvec);
+ if (folio_evictable(folio)) {
+ lruvec_del_folio(lruvec, folio);
+ folio_clear_unevictable(folio);
+ lruvec_add_folio(lruvec, folio);
pgrescued += nr_pages;
}
- SetPageLRU(page);
}
if (lruvec) {
--
2.11.0
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