memcg-v1: fully deprecate move_charge_at_immigrate

Patch series "memcg-v1: fully deprecate charge moving".

The memcg v1's charge moving feature has been deprecated for almost 2
years and the kernel warns if someone try to use it.  This warning has
been backported to all stable kernel and there have not been any report of
the warning or the request to support this feature anymore.  Let's proceed
to fully deprecate this feature.


This patch (of 6):

Proceed with the complete deprecation of memcg v1's charge moving feature.
The deprecation warning has been in the kernel for almost two years and
has been ported to all stable kernel since.  Now is the time to fully
deprecate this feature.

Link: https://lkml.kernel.org/r/20241025012304.2473312-1-shakeel.butt@linux.dev
Link: https://lkml.kernel.org/r/20241025012304.2473312-2-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 2 insertions, 12 deletions

diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
index f8744f5630bb..ef7e2a0ec66a 100644
--- a/mm/memcontrol-v1.c
+++ b/mm/memcontrol-v1.c
@@ -593,29 +593,19 @@ static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
 static u64 mem_cgroup_move_charge_read(struct cgroup_subsys_state *css,
 				struct cftype *cft)
 {
-	return mem_cgroup_from_css(css)->move_charge_at_immigrate;
+	return 0;
 }
 
 #ifdef CONFIG_MMU
 static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
 				 struct cftype *cft, u64 val)
 {
-	struct mem_cgroup *memcg = mem_cgroup_from_css(css);
-
 	pr_warn_once("Cgroup memory moving (move_charge_at_immigrate) is deprecated. "
 		     "Please report your usecase to linux-mm@kvack.org if you "
 		     "depend on this functionality.\n");
 
-	if (val & ~MOVE_MASK)
+	if (val != 0)
 		return -EINVAL;
-
-	/*
-	 * No kind of locking is needed in here, because ->can_attach() will
-	 * check this value once in the beginning of the process, and then carry
-	 * on with stale data. This means that changes to this value will only
-	 * affect task migrations starting after the change.
-	 */
-	memcg->move_charge_at_immigrate = val;
 	return 0;
 }
 #else