memcg: drop kmem.limit_in_bytes

commit 86327e8eb94c52eca4f93cfece2e29d1bf52acbf upstream.

kmem.limit_in_bytes (v1 way to limit kernel memory usage) has been
deprecated since 58056f77502f ("memcg, kmem: further deprecate
kmem.limit_in_bytes") merged in 5.16.  We haven't heard about any serious
users since then but it seems that the mere presence of the file is
causing more harm thatn good.  We (SUSE) have had several bug reports from
customers where Docker based containers started to fail because a write to
kmem.limit_in_bytes has failed.

This was unexpected because runc code only expects ENOENT (kmem disabled)
or EBUSY (tasks already running within cgroup).  So a new error code was
unexpected and the whole container startup failed.  This has been later
addressed by
https://github.com/opencontainers/runc/commit/52390d68040637dfc77f9fda6bbe70952423d380
so current Docker runtimes do not suffer from the problem anymore.  There
are still older version of Docker in use and likely hard to get rid of
completely.

Address this by wiping out the file completely and effectively get back to
pre 4.5 era and CONFIG_MEMCG_KMEM=n configuration.

I would recommend backporting to stable trees which have picked up
58056f77502f ("memcg, kmem: further deprecate kmem.limit_in_bytes").

[mhocko@suse.com: restore _KMEM switch case]
Link: https://lkml.kernel.org/r/ZKe5wxdbvPi5Cwd7@dhcp22.suse.cz
Link: https://lkml.kernel.org/r/20230704115240.14672-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
index 2524061836acc8a667ef7338b5d62ebde450c9f0..34911ce5e4b504eab4f5d4bd86dc3ecf6cfac470 100644 (file)
--- a/Documentation/admin-guide/cgroup-v1/memory.rst
+++ b/Documentation/admin-guide/cgroup-v1/memory.rst
@@ -91,8 +91,6 @@ 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          This knob is deprecated and writing to
-                                     it will return -ENOTSUPP.
  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 9ffcf80cf2524d31b028d80be734c2ee0f90e7d6..15f44cf4f939760caa3fc33d9967d32f5f21786a 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3841,10 +3841,6 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
                case _MEMSWAP:
                        ret = mem_cgroup_resize_max(memcg, nr_pages, true);
                        break;
-               case _KMEM:
-                       /* kmem.limit_in_bytes is deprecated. */
-                       ret = -EOPNOTSUPP;
-                       break;
                case _TCP:
                        ret = memcg_update_tcp_max(memcg, nr_pages);
                        break;
@@ -5055,12 +5051,6 @@ static struct cftype mem_cgroup_legacy_files[] = {
                .seq_show = memcg_numa_stat_show,
        },
 #endif
-       {
-               .name = "kmem.limit_in_bytes",
-               .private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
-               .write = mem_cgroup_write,
-               .read_u64 = mem_cgroup_read_u64,
-       },
        {
                .name = "kmem.usage_in_bytes",
                .private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),