memcg, kmem: further deprecate kmem.limit_in_bytes

The deprecation process of kmem.limit_in_bytes started with the commit
0158115f702 ("memcg, kmem: deprecate kmem.limit_in_bytes") which also
explains in detail the motivation behind the deprecation.  To summarize,
it is the unexpected behavior on hitting the kmem limit.  This patch
moves the deprecation process to the next stage by disallowing to set
the kmem limit.  In future we might just remove the kmem.limit_in_bytes
file completely.

[akpm@linux-foundation.org: s/ENOTSUPP/EOPNOTSUPP/]
[arnd@arndb.de: mark cancel_charge() inline]
  Link: https://lkml.kernel.org/r/20211022070542.679839-1-arnd@kernel.org

Link: https://lkml.kernel.org/r/20211019153408.2916808-1-shakeelb@google.com
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Vasily Averin <vvs@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 34 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e092cce3c96e..e4fcb6e55f75 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2771,8 +2771,7 @@ static inline int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	return try_charge_memcg(memcg, gfp_mask, nr_pages);
 }
 
-#if defined(CONFIG_MEMCG_KMEM) || defined(CONFIG_MMU)
-static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
+static inline void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
 	if (mem_cgroup_is_root(memcg))
 		return;
@@ -2781,7 +2780,6 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
 	if (do_memsw_account())
 		page_counter_uncharge(&memcg->memsw, nr_pages);
 }
-#endif
 
 static void commit_charge(struct page *page, struct mem_cgroup *memcg)
 {
@@ -3000,7 +2998,6 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg,
 static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
 				   unsigned int nr_pages)
 {
-	struct page_counter *counter;
 	struct mem_cgroup *memcg;
 	int ret;
 
@@ -3010,21 +3007,8 @@ static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
 	if (ret)
 		goto out;
 
-	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) &&
-	    !page_counter_try_charge(&memcg->kmem, nr_pages, &counter)) {
-
-		/*
-		 * Enforce __GFP_NOFAIL allocation because callers are not
-		 * prepared to see failures and likely do not have any failure
-		 * handling code.
-		 */
-		if (gfp & __GFP_NOFAIL) {
-			page_counter_charge(&memcg->kmem, nr_pages);
-			goto out;
-		}
-		cancel_charge(memcg, nr_pages);
-		ret = -ENOMEM;
-	}
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		page_counter_charge(&memcg->kmem, nr_pages);
 out:
 	css_put(&memcg->css);
 
@@ -3714,17 +3698,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
 }
 #endif /* CONFIG_MEMCG_KMEM */
 
-static int memcg_update_kmem_max(struct mem_cgroup *memcg,
-				 unsigned long max)
-{
-	int ret;
-
-	mutex_lock(&memcg_max_mutex);
-	ret = page_counter_set_max(&memcg->kmem, max);
-	mutex_unlock(&memcg_max_mutex);
-	return ret;
-}
-
 static int memcg_update_tcp_max(struct mem_cgroup *memcg, unsigned long max)
 {
 	int ret;
@@ -3790,10 +3763,8 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
 			ret = mem_cgroup_resize_max(memcg, nr_pages, true);
 			break;
 		case _KMEM:
-			pr_warn_once("kmem.limit_in_bytes is deprecated and will be removed. "
-				     "Please report your usecase to linux-mm@kvack.org if you "
-				     "depend on this functionality.\n");
-			ret = memcg_update_kmem_max(memcg, nr_pages);
+			/* kmem.limit_in_bytes is deprecated. */
+			ret = -EOPNOTSUPP;
 			break;
 		case _TCP:
 			ret = memcg_update_tcp_max(memcg, nr_pages);