vmscan, memcg: do softlimit reclaim also for targeted reclaim

Soft reclaim has been done only for the global reclaim (both background
and direct).  Since "memcg: integrate soft reclaim tighter with zone
shrinking code" there is no reason for this limitation anymore as the soft
limit reclaim doesn't use any special code paths and it is a part of the
zone shrinking code which is used by both global and targeted reclaims.

From the semantic point of view it is natural to consider soft limit
before touching all groups in the hierarchy tree which is touching the
hard limit because soft limit tells us where to push back when there is a
memory pressure.  It is not important whether the pressure comes from the
limit or imbalanced zones.

This patch simply enables soft reclaim unconditionally in
mem_cgroup_should_soft_reclaim so it is enabled for both global and
targeted reclaim paths.  mem_cgroup_soft_reclaim_eligible needs to learn
about the root of the reclaim to know where to stop checking soft limit
state of parents up the hierarchy.  Say we have

A (over soft limit)
 \
  B (below s.l., hit the hard limit)
 / \
C   D (below s.l.)

B is the source of the outside memory pressure now for D but we shouldn't
soft reclaim it because it is behaving well under B subtree and we can
still reclaim from C (pressumably it is over the limit).
mem_cgroup_soft_reclaim_eligible should therefore stop climbing up the
hierarchy at B (root of the memory pressure).

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Glauber Costa <glommer@openvz.org>
Reviewed-by: Tejun Heo <tj@kernel.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Ying Han <yinghan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 4b78661c68d0f56a2a09cc0849a763b3379356b5..d8dd6560621baf5b0e5ad094c818336752a66c9c 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -180,7 +180,8 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
        mem_cgroup_update_page_stat(page, idx, -1);
 }
 
-bool mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg);
+bool mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
+               struct mem_cgroup *root);
 
 void __mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
 static inline void mem_cgroup_count_vm_event(struct mm_struct *mm,
@@ -357,7 +358,8 @@ static inline void mem_cgroup_dec_page_stat(struct page *page,
 }
 
 static inline
-bool mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg)
+bool mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
+               struct mem_cgroup *root)
 {
        return false;
 }

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 62d94ab2f0ef0ff6e9713b5ccd73898d77b54942..a029dd7374f3e3735040632907f7952e0ded88bc 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1773,11 +1773,13 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
 #endif
 
 /*
- * A group is eligible for the soft limit reclaim if it is
- *     a) is over its soft limit
+ * A group is eligible for the soft limit reclaim under the given root
+ * hierarchy if
+ *     a) it is over its soft limit
  *     b) any parent up the hierarchy is over its soft limit
  */
-bool mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg)
+bool mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
+               struct mem_cgroup *root)
 {
        struct mem_cgroup *parent = memcg;
 
@@ -1785,12 +1787,14 @@ bool mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg)
                return true;
 
        /*
-        * If any parent up the hierarchy is over its soft limit then we
-        * have to obey and reclaim from this group as well.
+        * If any parent up to the root in the hierarchy is over its soft limit
+        * then we have to obey and reclaim from this group as well.
         */
        while((parent = parent_mem_cgroup(parent))) {
                if (res_counter_soft_limit_excess(&parent->res))
                        return true;
+               if (parent == root)
+                       break;
        }
 
        return false;

diff --git a/mm/vmscan.c b/mm/vmscan.c
index cfc8cefcfc2817774c4483ed8988241d1df6e6d4..d7f2e37940b53a1be7247970940a97934d317572 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -142,7 +142,7 @@ static bool global_reclaim(struct scan_control *sc)
 
 static bool mem_cgroup_should_soft_reclaim(struct scan_control *sc)
 {
-       return !mem_cgroup_disabled() && global_reclaim(sc);
+       return !mem_cgroup_disabled();
 }
 #else
 static bool global_reclaim(struct scan_control *sc)
@@ -2142,7 +2142,7 @@ __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
                        struct lruvec *lruvec;
 
                        if (soft_reclaim &&
-                           !mem_cgroup_soft_reclaim_eligible(memcg)) {
+                           !mem_cgroup_soft_reclaim_eligible(memcg, root)) {
                                memcg = mem_cgroup_iter(root, memcg, &reclaim);
                                continue;
                        }