mm: vmscan: do not scan anon pages if memcg swap limit is hit

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: NVladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

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__*/

mm/memcontrol.c

@@ -5748,6 +5748,19 @@ 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;

mm/vmscan.c

@@ -2004,7 +2004,7 @@ 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;
 	}