[PATCH v17 16/21] mm/swap: serialize memcg changes in pagevec_lru_move_fn

Alex Shi
2020-07-25T12:59:53Z

Hugh Dickins' found a memcg change bug on original version:
If we want to change the pgdat->lru_lock to memcg's lruvec lock, we have
to serialize mem_cgroup_move_account during pagevec_lru_move_fn. The
possible bad scenario would like:

cpu 0 cpu 1
lruvec = mem_cgroup_page_lruvec()
if (!isolate_lru_page())
mem_cgroup_move_account

spin_lock_irqsave(&lruvec->lru_lock <== wrong lock.

So we need the ClearPageLRU to block isolate_lru_page(), that serializes
the memcg change. and then removing the PageLRU check in move_fn callee
as the consequence.

Reported-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
mm/swap.c | 46 ++++++++++++++++++++++++++++++++++++----------
1 file changed, 36 insertions(+), 10 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 5092fe9c8c47..3029b3f74811 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -221,8 +221,14 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
spin_lock_irqsave(&pgdat->lru_lock, flags);
}

+ /* block memcg migration during page moving between lru */
+ if (!TestClearPageLRU(page))
+ continue;
+
lruvec = mem_cgroup_page_lruvec(page, pgdat);
(*move_fn)(page, lruvec);
+
+ SetPageLRU(page);
}
if (pgdat)
spin_unlock_irqrestore(&pgdat->lru_lock, flags);
@@ -232,7 +238,7 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,

static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec)
{
- if (PageLRU(page) && !PageUnevictable(page)) {
+ if (!PageUnevictable(page)) {
del_page_from_lru_list(page, lruvec, page_lru(page));
ClearPageActive(page);
add_page_to_lru_list_tail(page, lruvec, page_lru(page));
@@ -306,7 +312,7 @@ void lru_note_cost_page(struct page *page)

static void __activate_page(struct page *page, struct lruvec *lruvec)
{
- if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
+ if (!PageActive(page) && !PageUnevictable(page)) {
int lru = page_lru_base_type(page);
int nr_pages = hpage_nr_pages(page);

@@ -362,7 +368,8 @@ void activate_page(struct page *page)

page = compound_head(page);
spin_lock_irq(&pgdat->lru_lock);
- __activate_page(page, mem_cgroup_page_lruvec(page, pgdat));
+ if (PageLRU(page))
+ __activate_page(page, mem_cgroup_page_lruvec(page, pgdat));
spin_unlock_irq(&pgdat->lru_lock);
}
#endif
@@ -520,9 +527,6 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)
bool active;
int nr_pages = hpage_nr_pages(page);

- if (!PageLRU(page))
- return;
-
if (PageUnevictable(page))
return;

@@ -563,7 +567,7 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)

static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)
{
- if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
+ if (PageActive(page) && !PageUnevictable(page)) {
int lru = page_lru_base_type(page);
int nr_pages = hpage_nr_pages(page);

@@ -580,7 +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 (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
+ if (PageAnon(page) && PageSwapBacked(page) &&
!PageSwapCache(page) && !PageUnevictable(page)) {
bool active = PageActive(page);
int nr_pages = hpage_nr_pages(page);
@@ -654,7 +658,7 @@ void deactivate_file_page(struct page *page)
* In a workload with many unevictable page such as mprotect,
* unevictable page deactivation for accelerating reclaim is pointless.
*/
- if (PageUnevictable(page))
+ if (PageUnevictable(page) || !PageLRU(page))
return;

if (likely(get_page_unless_zero(page))) {
@@ -976,7 +980,29 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec)
*/
void __pagevec_lru_add(struct pagevec *pvec)
{
- pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn);
+ int i;
+ struct pglist_data *pgdat = NULL;
+ struct lruvec *lruvec;
+ unsigned long flags = 0;
+
+ for (i = 0; i < pagevec_count(pvec); i++) {
+ struct page *page = pvec->pages[i];
+ struct pglist_data *pagepgdat = page_pgdat(page);
+
+ if (pagepgdat != pgdat) {
+ if (pgdat)
+ spin_unlock_irqrestore(&pgdat->lru_lock, flags);
+ pgdat = pagepgdat;
+ spin_lock_irqsave(&pgdat->lru_lock, flags);
+ }
+
+ lruvec = mem_cgroup_page_lruvec(page, pgdat);
+ __pagevec_lru_add_fn(page, lruvec);
+ }
+ if (pgdat)
+ spin_unlock_irqrestore(&pgdat->lru_lock, flags);
+ release_pages(pvec->pages, pvec->nr);
+ pagevec_reinit(pvec);
}

/**
--
1.8.3.1