Re: [PATCH v2 2/4] memcg: initiate deprecation of v1 soft limit

["T.J. Mercier" <tjmercier@google.com>]

On Wed, Aug 14, 2024 at 3:00 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
>
> Memcg v1 provides soft limit functionality for the best effort memory
> sharing between multiple workloads on a system. It is usually triggered
> through kswapd and at the moment does not reclaim kernel memory.
>
> Memcg v2 provide more straightforward best effort (memory.low) and hard

"provides"

> protection (memory.min) functionalities. Let's initiate the deprecation
> of soft limit from v1 and gather if v2 needs something more to move the
> existing v1 users to v2 regarding soft limit.
>
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

Reviewed-by: T.J. Mercier <tjmercier@google.com>



> ---
> Changes since v1:
> - N/A
>
>  Documentation/admin-guide/cgroup-v1/memory.rst | 8 ++++++--
>  mm/memcontrol-v1.c                             | 3 +++
>  2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
> index 0114d758beab..6831c6c16e3f 100644
> --- a/Documentation/admin-guide/cgroup-v1/memory.rst
> +++ b/Documentation/admin-guide/cgroup-v1/memory.rst
> @@ -78,6 +78,8 @@ Brief summary of control files.
>   memory.memsw.max_usage_in_bytes     show max memory+Swap usage recorded
>   memory.soft_limit_in_bytes         set/show soft limit of memory usage
>                                      This knob is not available on CONFIG_PREEMPT_RT systems.
> +                                     This knob is deprecated and shouldn't be
> +                                     used.
>   memory.stat                        show various statistics
>   memory.use_hierarchy               set/show hierarchical account enabled
>                                       This knob is deprecated and shouldn't be
> @@ -701,8 +703,10 @@ For compatibility reasons writing 1 to memory.use_hierarchy will always pass::
>
>         # echo 1 > memory.use_hierarchy
>
> -7. Soft limits
> -==============
> +7. Soft limits (DEPRECATED)
> +===========================
> +
> +THIS IS DEPRECATED!
>
>  Soft limits allow for greater sharing of memory. The idea behind soft limits
>  is to allow control groups to use as much of the memory as needed, provided
> diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
> index b8e2ee454eaa..e0bb54e42011 100644
> --- a/mm/memcontrol-v1.c
> +++ b/mm/memcontrol-v1.c
> @@ -2458,6 +2458,9 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
>                 if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
>                         ret = -EOPNOTSUPP;
>                 } else {
> +                       pr_warn_once("soft_limit_in_bytes is deprecated and will be removed. "
> +                                    "Please report your usecase to linux-mm@kvack.org if you "
> +                                    "depend on this functionality.\n");
>                         WRITE_ONCE(memcg->soft_limit, nr_pages);
>                         ret = 0;
>                 }
> --
> 2.43.5
>