From: Michal Hocko <mhocko@suse.com>
Date: Thu, 21 Sep 2023 09:38:29 +0200
Subject: mm, memcg: reconsider kmem.limit_in_bytes deprecation
Git-commit: 4597648fddeadef5877610d693af11906aa666ac
Patch-mainline: v6.6-rc4
References: bsc#1208788 bsc#1213705
This reverts commits 86327e8eb94c ("memcg: drop kmem.limit_in_bytes") and
partially reverts 58056f77502f ("memcg, kmem: further deprecate
kmem.limit_in_bytes") which have incrementally removed support for the
kernel memory accounting hard limit. Unfortunately it has turned out that
there is still userspace depending on the existence of
memory.kmem.limit_in_bytes [1]. The underlying functionality is not
really required but the non-existent file just confuses the userspace
which fails in the result. The patch to fix this on the userspace side
has been submitted but it is hard to predict how it will propagate through
the maze of 3rd party consumers of the software.
Now, reverting alone 86327e8eb94c is not an option because there is
another set of userspace which cannot cope with ENOTSUPP returned when
writing to the file. Therefore we have to go and revisit 58056f77502f as
well. There are two ways to go ahead. Either we give up on the
deprecation and fully revert 58056f77502f as well or we can keep
kmem.limit_in_bytes but make the write a noop and warn about the fact.
This should work for both known breaking workloads which depend on the
existence but do not depend on the hard limit enforcement.
Note to backporters to stable trees. a8c49af3be5f ("memcg: add per-memcg
total kernel memory stat") introduced in 4.18 has added memcg_account_kmem
so the accounting is not done by obj_cgroup_charge_pages directly for v1
anymore. Prior kernels need to add it explicitly (thanks to Johannes for
pointing this out).
[akpm@linux-foundation.org: fix build - remove unused local]
Link: http://lkml.kernel.org/r/20230920081101.GA12096@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net [1]
Link: https://lkml.kernel.org/r/ZRE5VJozPZt9bRPy@dhcp22.suse.cz
Fixes: 86327e8eb94c ("memcg: drop kmem.limit_in_bytes")
Fixes: 58056f77502f ("memcg, kmem: further deprecate kmem.limit_in_bytes")
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Tejun heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Koutný <mkoutny@suse.com>
[mkoutny: Adjust context for SLE12-SP5]
---
Documentation/cgroup-v1/memory.txt | 7 +++++++
mm/memcontrol.c | 13 +++++++++++++
2 files changed, 20 insertions(+)
--- a/Documentation/cgroup-v1/memory.txt
+++ b/Documentation/cgroup-v1/memory.txt
@@ -78,6 +78,13 @@ 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 # Deprecated knob to set and read the kernel
+ # memory hard limit. Kernel hard limit is not
+ # supported since 5.16. Writing any value to
+ # do file will not have any effect same as if
+ # nokmem kernel parameter was specified.
+ # Kernel memory is still charged and reported
+ # by memory.kmem.usage_in_bytes.
memory.kmem.usage_in_bytes # show current kernel memory allocation
memory.kmem.failcnt # show the number of kernel memory usage hits limits
memory.kmem.max_usage_in_bytes # show max kernel memory usage recorded
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3029,6 +3029,13 @@ static ssize_t mem_cgroup_write(struct k
case _MEMSWAP:
ret = mem_cgroup_resize_memsw_limit(memcg, nr_pages);
break;
+ case _KMEM:
+ pr_warn_once("kmem.limit_in_bytes is deprecated and will be removed. "
+ "Writing any value to this file has no effect. "
+ "Please report your usecase to linux-mm@kvack.org if you "
+ "depend on this functionality.\n");
+ ret = 0;
+ break;
case _TCP:
ret = memcg_update_tcp_limit(memcg, nr_pages);
break;
@@ -4044,6 +4051,12 @@ static struct cftype mem_cgroup_legacy_f
},
#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,