linux-kernel - [PATCH] memcg, kmem: further deprecate kmem.limit_in

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Date:   Wed, 18 Nov 2020 09:57:26 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>, Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Shakeel Butt <shakeelb@...gle.com>
Subject: [PATCH] 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.

Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
---
 .../admin-guide/cgroup-v1/memory.rst          |  6 ++--
 mm/memcontrol.c                               | 35 +++----------------
 2 files changed, 6 insertions(+), 35 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
index 52688ae34461..cb993d80194d 100644
--- a/Documentation/admin-guide/cgroup-v1/memory.rst
+++ b/Documentation/admin-guide/cgroup-v1/memory.rst
@@ -87,10 +87,8 @@ Brief summary of control files.
  memory.oom_control		     set/show oom controls.
  memory.numa_stat		     show the number of memory usage per numa
 				     node
- memory.kmem.limit_in_bytes          set/show hard limit for kernel memory
-                                     This knob is deprecated and shouldn't be
-                                     used. It is planned that this be removed in
-                                     the foreseeable future.
+ memory.kmem.limit_in_bytes          This knob is deprecated and writing to
+                                     it will return -EINVAL.
  memory.kmem.usage_in_bytes          show current kernel memory allocation
  memory.kmem.failcnt                 show the number of kernel memory usage
 				     hits limits
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 45465c03a8d7..78d17b3181ad 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3075,28 +3075,14 @@ static void memcg_free_cache_id(int id)
 int __memcg_kmem_charge(struct mem_cgroup *memcg, gfp_t gfp,
 			unsigned int nr_pages)
 {
-	struct page_counter *counter;
 	int ret;
 
 	ret = try_charge(memcg, gfp, nr_pages);
 	if (ret)
 		return ret;
 
-	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);
-			return 0;
-		}
-		cancel_charge(memcg, nr_pages);
-		return -ENOMEM;
-	}
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		page_counter_charge(&memcg->kmem, nr_pages);
 	return 0;
 }
 
@@ -3769,17 +3755,6 @@ static void memcg_free_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;
@@ -3845,10 +3820,8 @@ 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@...ck.org if you "
-				     "depend on this functionality.\n");
-			ret = memcg_update_kmem_max(memcg, nr_pages);
+			/* kmem.limit_in_bytes is deprecated. */
+			ret = -EINVAL;
 			break;
 		case _TCP:
 			ret = memcg_update_tcp_max(memcg, nr_pages);
-- 
2.29.2.299.gdc1121823c-goog