[RFC PATCH v4 12/12] mm: lru: use lruvec lock to serialize memcg changes

From: Muchun Song <hidden>
Date: 2021-05-27 09:35:16
Also in: lkml
Subsystem: control group - memory resource controller (memcg), memory management, memory management - mglru (multi-gen lru), memory management - page allocator, memory management - reclaim, memory management - swap, the rest · Maintainers: Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt, Andrew Morton, Vlastimil Babka, Chris Li, Kairui Song, Linus Torvalds

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 <redacted>
---
 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 225e06c63ec1..c8505542c33e 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c

@@ -531,6 +531,7 @@ static struct lruvec *compact_lock_page_irqsave(struct page *page,
 
 	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 33aad9ed5071..289524aaf629 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -1318,12 +1318,38 @@ 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.
 	 */

@@ -1341,6 +1367,7 @@ 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;

@@ -1361,6 +1388,7 @@ 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;

@@ -5846,7 +5874,10 @@ 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 6260e0e11268..a254f0dcfe1d 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 5c30dffce768..a16b28da0878 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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