mm, memcg: create mem_cgroup_from_seq

This is the start of a series of patches similar to my earlier
DEFINE_MEMCG_MAX_OR_VAL work, but with less Macro Magic(tm).

There are a bunch of places we go from seq_file to mem_cgroup, which
currently requires manually getting the css, then getting the mem_cgroup
from the css.  It's in enough places now that having mem_cgroup_from_seq
makes sense (and also makes the next patch a bit nicer).

Link: http://lkml.kernel.org/r/20190124194050.GA31341@chrisdown.name
Signed-off-by: Chris Down <chris@chrisdown.name>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index b0eb29ea0d9c..1f3d880b7ca1 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -429,6 +429,11 @@ static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
 }
 struct mem_cgroup *mem_cgroup_from_id(unsigned short id);
 
+static inline struct mem_cgroup *mem_cgroup_from_seq(struct seq_file *m)
+{
+	return mem_cgroup_from_css(seq_css(m));
+}
+
 static inline struct mem_cgroup *lruvec_memcg(struct lruvec *lruvec)
 {
 	struct mem_cgroup_per_node *mz;
@@ -937,6 +942,11 @@ static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
 	return NULL;
 }
 
+static inline struct mem_cgroup *mem_cgroup_from_seq(struct seq_file *m)
+{
+	return NULL;
+}
+
 static inline struct mem_cgroup *lruvec_memcg(struct lruvec *lruvec)
 {
 	return NULL;