On Tue 09-04-13 14:13:15, Michal Hocko wrote:
> 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 semantic point of view it is even 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.
>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> mm/vmscan.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index ae3a387..cf729ca 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -141,7 +141,7 @@ static bool global_reclaim(struct scan_control *sc)
>
> static bool mem_cgroup_should_soft_reclaim(struct scan_control *sc)
> {
> - return global_reclaim(sc);
> + return true;
> }
> #else
> static bool global_reclaim(struct scan_control *sc)
This patch is not complete. We also need to update
mem_cgroup_soft_reclaim_eligible as well because we should ignore
parents that are above the current reclaim pressure. 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.
mem_cgroup_soft_reclaim_eligible should therefore stop climbing up the
hierarchy at B (root of the memory pressure).
---
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 1833c95..80ed1b6 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -179,7 +179,8 @@ 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,
@@ -356,7 +357,8 @@ 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 be86815..19b4cb7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1845,12 +1845,14 @@ int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
#endif
/*
- * A group is eligible for the soft limit reclaim if it is
+ * A group is eligible for the soft limit reclaim under given root hierarchy
+ * if it is
* a) doesn't have any soft limit set
* b) is over its soft limit
* c) 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;
@@ -1863,13 +1865,15 @@ 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 (parent->soft_limited &&
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 1fe9f81..471bf94 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1973,7 +1973,7 @@ __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;
}
--
Michal Hocko
SUSE Labs
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