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Date: Fri, 9 Apr 2021 20:29:59 +0800
From: Muchun Song <songmuchun@...edance.com>
To: guro@...com, hannes@...xchg.org, mhocko@...nel.org,
akpm@...ux-foundation.org, shakeelb@...gle.com,
vdavydov.dev@...il.com
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
duanxiongchun@...edance.com, fam.zheng@...edance.com,
bsingharora@...il.com, shy828301@...il.com,
alex.shi@...ux.alibaba.com, Muchun Song <songmuchun@...edance.com>
Subject: [RFC PATCH v2 18/18] 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 lock_page_lruvec*() 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/compaction.c | 1 +
mm/memcontrol.c | 31 +++++++++++++++++++++++++++++++
mm/swap.c | 41 +++++++++++------------------------------
mm/vmscan.c | 9 ++++-----
4 files changed, 47 insertions(+), 35 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 5fd37e14404f..382e40ccc694 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -531,6 +531,7 @@ compact_lock_page_lruvec_irqsave(struct page *page, unsigned long *flags,
spin_lock_irqsave(&lruvec->lru_lock, *flags);
out:
+ /* See the comments in lock_page_lruvec(). */
if (unlikely(lruvec_memcg(lruvec) != page_memcg(page))) {
spin_unlock_irqrestore(&lruvec->lru_lock, *flags);
goto retry;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 403b0743338b..1017e92f1d82 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1323,12 +1323,38 @@ struct lruvec *lock_page_lruvec(struct page *page)
lruvec = mem_cgroup_page_lruvec(page);
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 = mem_cgroup_page_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) != page_memcg(page))) {
spin_unlock(&lruvec->lru_lock);
goto retry;
}
/*
+ * When we reach here, it means that the page_memcg(page) is stable.
+ *
* Preemption is disabled in the internal of spin_lock, which can serve
* as RCU read-side critical sections.
*/
@@ -1346,6 +1372,7 @@ struct lruvec *lock_page_lruvec_irq(struct page *page)
lruvec = mem_cgroup_page_lruvec(page);
spin_lock_irq(&lruvec->lru_lock);
+ /* See the comments in lock_page_lruvec(). */
if (unlikely(lruvec_memcg(lruvec) != page_memcg(page))) {
spin_unlock_irq(&lruvec->lru_lock);
goto retry;
@@ -1366,6 +1393,7 @@ struct lruvec *lock_page_lruvec_irqsave(struct page *page, unsigned long *flags)
lruvec = mem_cgroup_page_lruvec(page);
spin_lock_irqsave(&lruvec->lru_lock, *flags);
+ /* See the comments in lock_page_lruvec(). */
if (unlikely(lruvec_memcg(lruvec) != page_memcg(page))) {
spin_unlock_irqrestore(&lruvec->lru_lock, *flags);
goto retry;
@@ -5687,7 +5715,10 @@ static int mem_cgroup_move_account(struct page *page,
obj_cgroup_get(to->objcg);
obj_cgroup_put(from->objcg);
+ /* See the comments in lock_page_lruvec(). */
+ spin_lock(&from_vec->lru_lock);
page->memcg_data = (unsigned long)to->objcg;
+ spin_unlock(&from_vec->lru_lock);
__unlock_page_objcg(from->objcg);
diff --git a/mm/swap.c b/mm/swap.c
index f3ce307d09fa..48e66a05c913 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -211,14 +211,8 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
for (i = 0; i < pagevec_count(pvec); i++) {
struct page *page = pvec->pages[i];
- /* block memcg migration during page moving between lru */
- if (!TestClearPageLRU(page))
- continue;
-
lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
(*move_fn)(page, lruvec);
-
- SetPageLRU(page);
}
if (lruvec)
unlock_page_lruvec_irqrestore(lruvec, flags);
@@ -228,7 +222,7 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec)
{
- if (!PageUnevictable(page)) {
+ if (PageLRU(page) && !PageUnevictable(page)) {
del_page_from_lru_list(page, lruvec);
ClearPageActive(page);
add_page_to_lru_list_tail(page, lruvec);
@@ -324,7 +318,7 @@ void lru_note_cost_page(struct page *page)
static void __activate_page(struct page *page, struct lruvec *lruvec)
{
- if (!PageActive(page) && !PageUnevictable(page)) {
+ if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
int nr_pages = thp_nr_pages(page);
del_page_from_lru_list(page, lruvec);
@@ -377,12 +371,9 @@ static void activate_page(struct page *page)
struct lruvec *lruvec;
page = compound_head(page);
- if (TestClearPageLRU(page)) {
- lruvec = lock_page_lruvec_irq(page);
- __activate_page(page, lruvec);
- unlock_page_lruvec_irq(lruvec);
- SetPageLRU(page);
- }
+ lruvec = lock_page_lruvec_irq(page);
+ __activate_page(page, lruvec);
+ unlock_page_lruvec_irq(lruvec);
}
#endif
@@ -537,6 +528,9 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)
bool active = PageActive(page);
int nr_pages = thp_nr_pages(page);
+ if (!PageLRU(page))
+ return;
+
if (PageUnevictable(page))
return;
@@ -574,7 +568,7 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)
static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)
{
- if (PageActive(page) && !PageUnevictable(page)) {
+ if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
int nr_pages = thp_nr_pages(page);
del_page_from_lru_list(page, lruvec);
@@ -590,7 +584,7 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)
static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec)
{
- if (PageAnon(page) && PageSwapBacked(page) &&
+ if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
!PageSwapCache(page) && !PageUnevictable(page)) {
int nr_pages = thp_nr_pages(page);
@@ -1055,20 +1049,7 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec)
*/
void __pagevec_lru_add(struct pagevec *pvec)
{
- int i;
- struct lruvec *lruvec = NULL;
- unsigned long flags = 0;
-
- for (i = 0; i < pagevec_count(pvec); i++) {
- struct page *page = pvec->pages[i];
-
- lruvec = relock_page_lruvec_irqsave(page, lruvec, &flags);
- __pagevec_lru_add_fn(page, lruvec);
- }
- if (lruvec)
- unlock_page_lruvec_irqrestore(lruvec, flags);
- release_pages(pvec->pages, pvec->nr);
- pagevec_reinit(pvec);
+ pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn);
}
/**
diff --git a/mm/vmscan.c b/mm/vmscan.c
index af0fc8110bdc..12c2ea6cb6f3 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4469,18 +4469,17 @@ void check_move_unevictable_pages(struct pagevec *pvec)
nr_pages = thp_nr_pages(page);
pgscanned += nr_pages;
- /* block memcg migration during page moving between lru */
- if (!TestClearPageLRU(page))
+ lruvec = relock_page_lruvec_irq(page, lruvec);
+
+ if (!PageLRU(page) || !PageUnevictable(page))
continue;
- lruvec = relock_page_lruvec_irq(page, lruvec);
- if (page_evictable(page) && PageUnevictable(page)) {
+ if (page_evictable(page)) {
del_page_from_lru_list(page, lruvec);
ClearPageUnevictable(page);
add_page_to_lru_list(page, lruvec);
pgrescued += nr_pages;
}
- SetPageLRU(page);
}
if (lruvec) {
--
2.11.0
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