Re: [PATCH v2 4/4] memcg: initiate deprecation of pressure_level

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

On Wed, Aug 14, 2024 at 3:00 PM Shakeel Butt <shakeel.butt@linux.dev> wrote:
>
> The pressure_level in memcg v1 provides memory pressure notifications to
> the user space. At the moment it provides notifications for three levels
> of memory pressure i.e. low, medium and critical, which are defined
> based on internal memory reclaim implementation details. More
> specifically the ratio or scanned and reclaimed pages during a memory

"ratio of"

> reclaim. However this is not robust as there are workloads with mostly
> unreclaimable user memory or kernel memory.
>
> For v2, the users can use PSI for memory pressure status of the system
> or the cgroup. Let's start the deprecation process for pressure_level
> and add warnings to gather the info on how the current users are using
> this interface and how they can be used to PSI.
>
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

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


> ---
> Changes since v1:
> - Fix build (T.J. Mercier)
>
>  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 0042206414c8..270501db9f4e 100644
> --- a/Documentation/admin-guide/cgroup-v1/memory.rst
> +++ b/Documentation/admin-guide/cgroup-v1/memory.rst
> @@ -86,6 +86,8 @@ Brief summary of control files.
>                                       used.
>   memory.force_empty                 trigger forced page reclaim
>   memory.pressure_level              set memory pressure notifications
> +                                     This knob is deprecated and shouldn't be
> +                                     used.
>   memory.swappiness                  set/show swappiness parameter of vmscan
>                                      (See sysctl's vm.swappiness)
>   memory.move_charge_at_immigrate     set/show controls of moving charges
> @@ -898,8 +900,10 @@ At reading, current status of OOM is shown.
>            The number of processes belonging to this cgroup killed by any
>            kind of OOM killer.
>
> -11. Memory Pressure
> -===================
> +11. Memory Pressure (DEPRECATED)
> +================================
> +
> +THIS IS DEPRECATED!
>
>  The pressure level notifications can be used to monitor the memory
>  allocation cost; based on the pressure, applications can implement
> diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
> index 334a02597d9a..52aecdae2c28 100644
> --- a/mm/memcontrol-v1.c
> +++ b/mm/memcontrol-v1.c
> @@ -1913,6 +1913,9 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
>                 event->register_event = mem_cgroup_oom_register_event;
>                 event->unregister_event = mem_cgroup_oom_unregister_event;
>         } else if (!strcmp(name, "memory.pressure_level")) {
> +               pr_warn_once("pressure_level is deprecated and will be removed. "
> +                            "Please report your usecase to linux-mm-@kvack.org "
> +                            "if you depend on this functionality. \n");
>                 event->register_event = vmpressure_register_event;
>                 event->unregister_event = vmpressure_unregister_event;
>         } else if (!strcmp(name, "memory.memsw.usage_in_bytes")) {
> --
> 2.43.5
>