Revert "memcg: drop kmem.limit_in_bytes"

This reverts commit 21ef9e11205fca43785eecf7d4a99528d4de5701 which is
commit 86327e8eb94c52eca4f93cfece2e29d1bf52acbf upstream.

It breaks existing runc systems, as the tool always thinks the file
should be present.

Reported-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Link: https://lore.kernel.org/r/20230920081101.GA12096@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net
Cc: Michal Hocko <mhocko@suse.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: 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 34911ce..2524061 100644 (file)
--- a/Documentation/admin-guide/cgroup-v1/memory.rst
+++ b/Documentation/admin-guide/cgroup-v1/memory.rst
@@ -91,6 +91,8 @@ 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          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 0a403b2..67b6d82 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3841,6 +3841,10 @@ 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;
@@ -5052,6 +5056,12 @@ static struct cftype mem_cgroup_legacy_files[] = {
        },
 #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),
                .read_u64 = mem_cgroup_read_u64,