[PATCH v2 5/7] mm: vmscan: do not scan anon pages if memcg swap limit is hit

[Vladimir Davydov <vdavydov@virtuozzo.com>]

We don't scan anonymous memory if we ran out of swap, neither should we
do it in case memcg swap limit is hit, because swap out is impossible
anyway.

Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
---
Changes in v2:
 - Do not check swap limit on the legacy hierarchy.

 include/linux/swap.h |  6 ++++++
 mm/memcontrol.c      | 13 +++++++++++++
 mm/vmscan.c          |  2 +-
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index f8fb4e06c4bd..c544998dfbe7 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -551,6 +551,7 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
 extern void mem_cgroup_swapout(struct page *page, swp_entry_t entry);
 extern int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry);
 extern void mem_cgroup_uncharge_swap(swp_entry_t entry);
+extern long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg);
 #else
 static inline void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 {
@@ -565,6 +566,11 @@ static inline int mem_cgroup_try_charge_swap(struct page *page,
 static inline void mem_cgroup_uncharge_swap(swp_entry_t entry)
 {
 }
+
+static inline long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg)
+{
+	return get_nr_swap_pages();
+}
 #endif
 
 #endif /* __KERNEL__*/
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 567b56da2c23..e0e498f5ca32 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5736,6 +5736,19 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry)
 	rcu_read_unlock();
 }
 
+long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg)
+{
+	long nr_swap_pages = get_nr_swap_pages();
+
+	if (!do_swap_account || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return nr_swap_pages;
+	for (; memcg != root_mem_cgroup; memcg = parent_mem_cgroup(memcg))
+		nr_swap_pages = min_t(long, nr_swap_pages,
+				      READ_ONCE(memcg->swap.limit) -
+				      page_counter_read(&memcg->swap));
+	return nr_swap_pages;
+}
+
 /* for remember boot option*/
 #ifdef CONFIG_MEMCG_SWAP_ENABLED
 static int really_do_swap_account __initdata = 1;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b220e6cda25d..ab52d865d922 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1995,7 +1995,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
 		force_scan = true;
 
 	/* If we have no swap space, do not bother scanning anon pages. */
-	if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
+	if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
 		scan_balance = SCAN_FILE;
 		goto out;
 	}
-- 
2.1.4