On Tue, Jul 04, 2023 at 01:52:40PM +0200, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> 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").
>
> Cc: stable
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> Documentation/admin-guide/cgroup-v1/memory.rst | 2 --
> mm/memcontrol.c | 13 -------------
> 2 files changed, 15 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
> index 47d1d7d932a8..b92c71f39172 100644
> --- a/Documentation/admin-guide/cgroup-v1/memory.rst
> +++ b/Documentation/admin-guide/cgroup-v1/memory.rst
> @@ -92,8 +92,6 @@ 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 4b27e245a055..a0d3ed8d02e2 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3750,9 +3750,6 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css,
> case _MEMSWAP:
> counter = &memcg->memsw;
> break;
> - case _KMEM:
> - counter = &memcg->kmem;
> - break;
> case _TCP:
> counter = &memcg->tcpmem;
> break;
This case is still needed for the remaining kmem files:
{
.name = "kmem.usage_in_bytes",
.private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),
.read_u64 = mem_cgroup_read_u64,
},
{
.name = "kmem.failcnt",
.private = MEMFILE_PRIVATE(_KMEM, RES_FAILCNT),
.write = mem_cgroup_reset,
.read_u64 = mem_cgroup_read_u64,
},
{
.name = "kmem.max_usage_in_bytes",
.private = MEMFILE_PRIVATE(_KMEM, RES_MAX_USAGE),
.write = mem_cgroup_reset,
.read_u64 = mem_cgroup_read_u64,
},
otherwise they BUG() when reading.
Without this hunk, the patch looks good to me.
