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Subject[PATCH v5 01/11] mm: memcontrol: remove dead code and comments
Date
Since no-hierarchy mode is deprecated after

commit bef8620cd8e0 ("mm: memcg: deprecate the non-hierarchical mode")

so parent_mem_cgroup() cannot return a NULL except root memcg, however, root
memcg cannot be offline, so it is safe to drop the check of returned value
of parent_mem_cgroup(). Remove those dead code.

The comments in memcg_offline_kmem() above memcg_reparent_list_lrus() are
out of date since

commit 5abc1e37afa0 ("mm: list_lru: allocate list_lru_one only when needed")

There is no ordering requirement between memcg_reparent_list_lrus() and
memcg_reparent_objcgs(), so remove those outdated comments.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
include/linux/memcontrol.h | 3 +--
mm/memcontrol.c | 16 ----------------
mm/vmscan.c | 6 +-----
3 files changed, 2 insertions(+), 23 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 89b14729d59f..0833be256134 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -851,8 +851,7 @@ static inline struct mem_cgroup *lruvec_memcg(struct lruvec *lruvec)
* parent_mem_cgroup - find the accounting parent of a memcg
* @memcg: memcg whose parent to find
*
- * Returns the parent memcg, or NULL if this is the root or the memory
- * controller is in legacy no-hierarchy mode.
+ * Returns the parent memcg, or NULL if this is the root.
*/
static inline struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg)
{
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 598fece89e2b..13da256ff2e4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3622,17 +3622,7 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
return;

parent = parent_mem_cgroup(memcg);
- if (!parent)
- parent = root_mem_cgroup;
-
memcg_reparent_objcgs(memcg, parent);
-
- /*
- * After we have finished memcg_reparent_objcgs(), all list_lrus
- * corresponding to this cgroup are guaranteed to remain empty.
- * The ordering is imposed by list_lru_node->lock taken by
- * memcg_reparent_list_lrus().
- */
memcg_reparent_list_lrus(memcg, parent);
}
#else
@@ -6593,10 +6583,6 @@ void mem_cgroup_calculate_protection(struct mem_cgroup *root,
return;

parent = parent_mem_cgroup(memcg);
- /* No parent means a non-hierarchical mode on v1 memcg */
- if (!parent)
- return;
-
if (parent == root) {
memcg->memory.emin = READ_ONCE(memcg->memory.min);
memcg->memory.elow = READ_ONCE(memcg->memory.low);
@@ -7050,8 +7036,6 @@ static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
break;
}
memcg = parent_mem_cgroup(memcg);
- if (!memcg)
- memcg = root_mem_cgroup;
}
return memcg;
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1678802e03e7..8c6054e06087 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -409,13 +409,9 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
{
int i, nid;
long nr;
- struct mem_cgroup *parent;
+ struct mem_cgroup *parent = parent_mem_cgroup(memcg);
struct shrinker_info *child_info, *parent_info;

- parent = parent_mem_cgroup(memcg);
- if (!parent)
- parent = root_mem_cgroup;
-
/* Prevent from concurrent shrinker_info expand */
down_read(&shrinker_rwsem);
for_each_node(nid) {
--
2.11.0
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