[PATCH v6 09/16] mm: memcontrol: move memcg_online_kmem() to mem_cgroup_css_online()

[Muchun Song <songmuchun@bytedance.com>]

It will simplify the code if moving memcg_online_kmem() to
mem_cgroup_css_online() and do not need to set ->kmemcg_id
to -1 to indicate the memcg is offline. In the next patch,
->kmemcg_id will be used to sync list lru reparenting which
requires not to change ->kmemcg_id.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 mm/memcontrol.c | 37 ++++++++++++++++---------------------
 1 file changed, 16 insertions(+), 21 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ffc5f0798de1..5bdf5184681c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3616,7 +3616,8 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
 	if (cgroup_memory_nokmem)
 		return 0;
 
-	BUG_ON(memcg->kmemcg_id >= 0);
+	if (unlikely(mem_cgroup_is_root(memcg)))
+		return 0;
 
 	memcg_id = memcg_alloc_cache_id();
 	if (memcg_id < 0)
@@ -3642,7 +3643,10 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
 	struct mem_cgroup *parent;
 	int kmemcg_id;
 
-	if (memcg->kmemcg_id == -1)
+	if (cgroup_memory_nokmem)
+		return;
+
+	if (unlikely(mem_cgroup_is_root(memcg)))
 		return;
 
 	parent = parent_mem_cgroup(memcg);
@@ -3652,7 +3656,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
 	memcg_reparent_objcgs(memcg, parent);
 
 	kmemcg_id = memcg->kmemcg_id;
-	BUG_ON(kmemcg_id < 0);
 
 	/*
 	 * After we have finished memcg_reparent_objcgs(), all list_lrus
@@ -3663,7 +3666,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
 	memcg_drain_all_list_lrus(kmemcg_id, parent);
 
 	memcg_free_cache_id(kmemcg_id);
-	memcg->kmemcg_id = -1;
 }
 #else
 static int memcg_online_kmem(struct mem_cgroup *memcg)
@@ -5178,7 +5180,6 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 {
 	struct mem_cgroup *parent = mem_cgroup_from_css(parent_css);
 	struct mem_cgroup *memcg, *old_memcg;
-	long error = -ENOMEM;
 
 	old_memcg = set_active_memcg(parent);
 	memcg = mem_cgroup_alloc();
@@ -5207,34 +5208,26 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 		return &memcg->css;
 	}
 
-	/* The following stuff does not apply to the root */
-	error = memcg_online_kmem(memcg);
-	if (error)
-		goto fail;
-
 	if (cgroup_subsys_on_dfl(memory_cgrp_subsys) && !cgroup_memory_nosocket)
 		static_branch_inc(&memcg_sockets_enabled_key);
 
 	return &memcg->css;
-fail:
-	mem_cgroup_id_remove(memcg);
-	mem_cgroup_free(memcg);
-	return ERR_PTR(error);
 }
 
 static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
 
+	if (memcg_online_kmem(memcg))
+		goto remove_id;
+
 	/*
 	 * A memcg must be visible for expand_shrinker_info()
 	 * by the time the maps are allocated. So, we allocate maps
 	 * here, when for_each_mem_cgroup() can't skip it.
 	 */
-	if (alloc_shrinker_info(memcg)) {
-		mem_cgroup_id_remove(memcg);
-		return -ENOMEM;
-	}
+	if (alloc_shrinker_info(memcg))
+		goto offline_kmem;
 
 	/* Online state pins memcg ID, memcg ID pins CSS */
 	refcount_set(&memcg->id.ref, 1);
@@ -5244,6 +5237,11 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css)
 		queue_delayed_work(system_unbound_wq, &stats_flush_dwork,
 				   2UL*HZ);
 	return 0;
+offline_kmem:
+	memcg_offline_kmem(memcg);
+remove_id:
+	mem_cgroup_id_remove(memcg);
+	return -ENOMEM;
 }
 
 static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
@@ -5301,9 +5299,6 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
 	cancel_work_sync(&memcg->high_work);
 	mem_cgroup_remove_from_trees(memcg);
 	free_shrinker_info(memcg);
-
-	/* Need to offline kmem if online_css() fails */
-	memcg_offline_kmem(memcg);
 	mem_cgroup_free(memcg);
 }
 
-- 
2.11.0