Soft limit reclaim has to check the whole reclaim hierarchy while doing
the first pass of the reclaim. This leads to a higher system time which
can be visible especially when there are many groups in the hierarchy.
- TODO put testing results here
This patch adds a per-memcg counter of children in excess. It also
restores MEM_CGROUP_TARGET_SOFTLIMIT into mem_cgroup_event_ratelimit for
a proper batching.
If a group crosses soft limit for the first time it increases parent's
children_in_excess up the hierarchy. The similarly if a group gets below
the limit it will decrease the counter. The transition phase is recorded
in soft_contributed flag.
mem_cgroup_soft_reclaim_eligible then uses this information to better
decide whether to skip the node or the whole subtree. The rule is
simple. Skip the node with a children in excess or skip the whole subtree
otherwise.
Signed-off-by: Michal Hocko <mho...@suse.cz>
---
mm/memcontrol.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 51 insertions(+)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 981ee12..60b48bc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -136,6 +136,7 @@ static const char * const mem_cgroup_lru_names[] = {
*/
enum mem_cgroup_events_target {
MEM_CGROUP_TARGET_THRESH,
+ MEM_CGROUP_TARGET_SOFTLIMIT,
MEM_CGROUP_TARGET_NUMAINFO,
MEM_CGROUP_NTARGETS,
};
@@ -355,6 +356,10 @@ struct mem_cgroup {
atomic_t numainfo_updating;
#endif
+ spinlock_t soft_lock;
+ bool soft_contributed;
+ atomic_t children_in_excess;
+
/*
* Per cgroup active and inactive list, similar to the
* per zone LRU lists.
@@ -890,6 +895,9 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup
*memcg,
case MEM_CGROUP_TARGET_THRESH:
next = val + THRESHOLDS_EVENTS_TARGET;
break;
+ case MEM_CGROUP_TARGET_SOFTLIMIT:
+ next = val + SOFTLIMIT_EVENTS_TARGET;
+ break;
case MEM_CGROUP_TARGET_NUMAINFO:
next = val + NUMAINFO_EVENTS_TARGET;
break;
@@ -902,6 +910,34 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup
*memcg,
return false;
}
+static void mem_cgroup_update_soft_limit(struct mem_cgroup *memcg)
+{
+ unsigned long long excess = res_counter_soft_limit_excess(&memcg->res);
+ struct mem_cgroup *parent = memcg;
+ int delta = 0;
+
+ spin_lock(&memcg->soft_lock);
+ if (excess) {
+ if (!memcg->soft_contributed) {
+ delta = 1;
+ memcg->soft_contributed = true;
+ }
+ } else {
+ if (memcg->soft_contributed) {
+ delta = -1;
+ memcg->soft_contributed = false;
+ }
+ }
+
+ /*
+ * Necessary to update all ancestors when hierarchy is used
+ * because their event counter is not touched.
+ */
+ while (delta && (parent = parent_mem_cgroup(parent)))
+ atomic_add(delta, &parent->children_in_excess);
+ spin_unlock(&memcg->soft_lock);
+}
+
/*
* Check events in order.
*
@@ -912,8 +948,11 @@ static void memcg_check_events(struct mem_cgroup *memcg,
struct page *page)
/* threshold event is triggered in finer grain than soft limit */
if (unlikely(mem_cgroup_event_ratelimit(memcg,
MEM_CGROUP_TARGET_THRESH))) {
+ bool do_softlimit;
bool do_numainfo __maybe_unused;
+ do_softlimit = mem_cgroup_event_ratelimit(memcg,
+ MEM_CGROUP_TARGET_SOFTLIMIT);
#if MAX_NUMNODES > 1
do_numainfo = mem_cgroup_event_ratelimit(memcg,
MEM_CGROUP_TARGET_NUMAINFO);
@@ -921,6 +960,8 @@ static void memcg_check_events(struct mem_cgroup *memcg,
struct page *page)
preempt_enable();
mem_cgroup_threshold(memcg);
+ if (unlikely(do_softlimit))
+ mem_cgroup_update_soft_limit(memcg);
#if MAX_NUMNODES > 1
if (unlikely(do_numainfo))
atomic_inc(&memcg->numainfo_events);
@@ -1894,6 +1935,9 @@ int mem_cgroup_select_victim_node(struct mem_cgroup
*memcg)
* hierarchy if
* a) it is over its soft limit
* b) any parent up the hierarchy is over its soft limit
+ *
+ * If the given group doesn't have any children over the limit then it
+ * doesn't make any sense to iterate its subtree.
*/
enum mem_cgroup_filter_t
mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
@@ -1915,6 +1959,8 @@ mem_cgroup_soft_reclaim_eligible(struct mem_cgroup *memcg,
break;
}
+ if (!atomic_read(&memcg->children_in_excess))
+ return SKIP_TREE;
return SKIP;
}
@@ -6061,6 +6107,7 @@ mem_cgroup_css_alloc(struct cgroup *cont)
mutex_init(&memcg->thresholds_lock);
spin_lock_init(&memcg->move_lock);
vmpressure_init(&memcg->vmpressure);
+ spin_lock_init(&memcg->soft_lock);
return &memcg->css;
@@ -6150,6 +6197,10 @@ static void mem_cgroup_css_offline(struct cgroup *cont)
mem_cgroup_invalidate_reclaim_iterators(memcg);
mem_cgroup_reparent_charges(memcg);
+ if (memcg->soft_contributed) {
+ while ((memcg = parent_mem_cgroup(memcg)))
+ atomic_dec(&memcg->children_in_excess);
+ }
mem_cgroup_destroy_all_caches(memcg);
}
--
1.7.10.4
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