mm/vmscan: Consider anonymous pages without swap

Reclaim anonymous pages if a migration path is available now that demotion
provides a non-swap recourse for reclaiming anon pages.

Note that this check is subtly different from the can_age_anon_pages()
checks.  This mechanism checks whether a specific page in a specific
context can actually be reclaimed, given current swap space and cgroup
limits.

can_age_anon_pages() is a much simpler and more preliminary check which
just says whether there is a possibility of future reclaim.

[kbusch@kernel.org: v11]
Link: https://lkml.kernel.org/r/20210715055145.195411-8-ying.huang@intel.com
Link: https://lkml.kernel.org/r/20210721063926.3024591-7-ying.huang@intel.com
Link: https://lkml.kernel.org/r/20210715055145.195411-8-ying.huang@intel.com
Cc: Keith Busch <kbusch@kernel.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Xu <weixugc@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index c84aba2..b097076 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -524,7 +524,7 @@ static long add_nr_deferred(long nr, struct shrinker *shrinker,
 
 static bool can_demote(int nid, struct scan_control *sc)
 {
-       if (sc->no_demotion)
+       if (sc && sc->no_demotion)
                return false;
        if (next_demotion_node(nid) == NUMA_NO_NODE)
                return false;
@@ -533,6 +533,31 @@ static bool can_demote(int nid, struct scan_control *sc)
        return false;
 }
 
+static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,
+                                         int nid,
+                                         struct scan_control *sc)
+{
+       if (memcg == NULL) {
+               /*
+                * For non-memcg reclaim, is there
+                * space in any swap device?
+                */
+               if (get_nr_swap_pages() > 0)
+                       return true;
+       } else {
+               /* Is the memcg below its swap limit? */
+               if (mem_cgroup_get_nr_swap_pages(memcg) > 0)
+                       return true;
+       }
+
+       /*
+        * The page can not be swapped.
+        *
+        * Can it be reclaimed from this node via demotion?
+        */
+       return can_demote(nid, sc);
+}
+
 /*
  * This misses isolated pages which are not accounted for to save counters.
  * As the data only determines if reclaim or compaction continues, it is
@@ -544,7 +569,7 @@ unsigned long zone_reclaimable_pages(struct zone *zone)
 
        nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
                zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
-       if (get_nr_swap_pages() > 0)
+       if (can_reclaim_anon_pages(NULL, zone_to_nid(zone), NULL))
                nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
                        zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
 
@@ -2541,6 +2566,7 @@ enum scan_balance {
 static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
                           unsigned long *nr)
 {
+       struct pglist_data *pgdat = lruvec_pgdat(lruvec);
        struct mem_cgroup *memcg = lruvec_memcg(lruvec);
        unsigned long anon_cost, file_cost, total_cost;
        int swappiness = mem_cgroup_swappiness(memcg);
@@ -2551,7 +2577,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
        enum lru_list lru;
 
        /* If we have no swap space, do not bother scanning anon pages. */
-       if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
+       if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
                scan_balance = SCAN_FILE;
                goto out;
        }
@@ -2929,7 +2955,7 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
         */
        pages_for_compaction = compact_gap(sc->order);
        inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
-       if (get_nr_swap_pages() > 0)
+       if (can_reclaim_anon_pages(NULL, pgdat->node_id, sc))
                inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
 
        return inactive_lru_pages > pages_for_compaction;