[PATCH rfc 2/5] mm: memcontrol: introduce mem_cgroup_ino() and mem_cgroup_get_from_ino()

[Roman Gushchin <roman.gushchin@linux.dev>]

Shrinker sysfs requires a way to represent memory cgroups without
using full paths, both for displaying information and getting input
from a user.

Cgroup inode numbers is a perfect way, used by e.g. bpf.

This commit adds a couple of helper functions, which will be used to
represent and interact with memcg-aware shrinkers using shrinkers sysfs.

Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
---
 include/linux/memcontrol.h |  9 +++++++++
 mm/memcontrol.c            | 23 +++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index cc16ba262464..299472046000 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -838,6 +838,15 @@ static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
 }
 struct mem_cgroup *mem_cgroup_from_id(unsigned short id);
 
+#ifdef CONFIG_SHRINKER_DEBUG
+static inline unsigned long mem_cgroup_ino(struct mem_cgroup *memcg)
+{
+	return cgroup_ino(memcg->css.cgroup);
+}
+
+struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino);
+#endif
+
 static inline struct mem_cgroup *mem_cgroup_from_seq(struct seq_file *m)
 {
 	return mem_cgroup_from_css(seq_css(m));
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4a3e1300c5a1..030dd637ec7a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5023,6 +5023,29 @@ struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
 	return idr_find(&mem_cgroup_idr, id);
 }
 
+#ifdef CONFIG_SHRINKER_DEBUG
+struct mem_cgroup *mem_cgroup_get_from_ino(unsigned long ino)
+{
+	struct cgroup *cgrp;
+	struct cgroup_subsys_state *css;
+	struct mem_cgroup *memcg;
+
+	cgrp = cgroup_get_from_id(ino);
+	if (!cgrp)
+		return ERR_PTR(-ENOENT);
+
+	css = cgroup_get_e_css(cgrp, &memory_cgrp_subsys);
+	if (css)
+		memcg = container_of(css, struct mem_cgroup, css);
+	else
+		memcg = ERR_PTR(-ENOENT);
+
+	cgroup_put(cgrp);
+
+	return memcg;
+}
+#endif
+
 static int alloc_mem_cgroup_per_node_info(struct mem_cgroup *memcg, int node)
 {
 	struct mem_cgroup_per_node *pn;
-- 
2.35.1