[RFC PATCH 4/4] mm: memcg: pmc: support oom release

[Huan Yang <link@vivo.com>]

This patch let each enabled pmc's memcg register a oom listener,
so if oom will trigger, release all hold pages.

Signed-off-by: Huan Yang <link@vivo.com>
---
 include/linux/mmzone.h |  3 +++
 mm/memcontrol.c        | 31 +++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b56dd462232b..640a9cf51791 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -622,6 +622,9 @@ struct mem_cgroup_per_node_cache {
 	unsigned int reaper_wait;
 	struct delayed_work reaper_work;
 
+	/* listen oom event, release hold cache */
+	struct notifier_block oom_nb;
+
 	/* max number to hold page, unit page, default 100MB */
 #define DEFAULT_PMC_HOLD_LIMIX ((100 << 20) >> PAGE_SHIFT)
 	unsigned int hold_limit;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ae6917de91cc..3dfb2a17c1fd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7101,6 +7101,33 @@ static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf,
 	return nbytes;
 }
 
+/**
+ * This function listen to oom event, if oom will trigger, check and release
+ * all holded pages.
+ */
+static int pmc_oom_notify(struct notifier_block *self,
+				     unsigned long notused, void *nfreed)
+{
+	struct mem_cgroup_per_node_cache *node_cachep =
+		container_of(self, struct mem_cgroup_per_node_cache, oom_nb);
+	struct mem_cgroup *memcg = node_cachep->memcg;
+
+	unsigned long *nf = (unsigned long *)nfreed;
+
+	rcu_read_lock();
+	if (!css_tryget(&memcg->css)) {
+		rcu_read_unlock();
+		return NOTIFY_STOP;
+	}
+	rcu_read_unlock();
+
+	nf += mem_cgroup_release_cache(node_cachep);
+
+	css_put(&memcg->css);
+
+	return NOTIFY_OK;
+}
+
 /**
  * This function use to reaper all cache pages by cycling scan.
  * The scan interval time depends on @reaper_wait which can set by `keys` nest
@@ -7176,6 +7203,9 @@ static int __enable_mem_cgroup_cache(struct mem_cgroup *memcg)
 		p->allow_watermark = DEFAULT_PMC_GAP_WATERMARK;
 		p->reaper_wait = DEFAULT_PMC_REAPER_TIME;
 
+		p->oom_nb.notifier_call = pmc_oom_notify;
+		register_oom_notifier(&p->oom_nb);
+
 		atomic_inc(&pmc_nr_enabled);
 
 		INIT_DELAYED_WORK(&p->reaper_work, pmc_reaper);
@@ -7222,6 +7252,7 @@ static int __disable_mem_cgroup_cache(struct mem_cgroup *memcg)
 
 		p = nodeinfo->cachep;
 
+		unregister_oom_notifier(&p->oom_nb);
 		cancel_delayed_work_sync(&p->reaper_work);
 		mem_cgroup_release_cache(p);
 
-- 
2.45.2