On Thu 17-02-22 10:47:59, Sebastian Andrzej Siewior wrote:
> During the integration of PREEMPT_RT support, the code flow around
> memcg_check_events() resulted in `twisted code'. Moving the code around
> and avoiding then would then lead to an additional local-irq-save
> section within memcg_check_events(). While looking better, it adds a
> local-irq-save section to code flow which is usually within an
> local-irq-off block on non-PREEMPT_RT configurations.
>
> The threshold event handler is a deprecated memcg v1 feature. Instead of
> trying to get it to work under PREEMPT_RT just disable it. There should
> be no users on PREEMPT_RT. From that perspective it makes even less
> sense to get it to work under PREEMPT_RT while having zero users.
>
> Make memory.soft_limit_in_bytes and cgroup.event_control return
> -EOPNOTSUPP on PREEMPT_RT. Make an empty memcg_check_events() and
> memcg_write_event_control() which return only -EOPNOTSUPP on PREEMPT_RT.
> Document that the two knobs are disabled on PREEMPT_RT.
>
> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Suggested-by: Michal Koutný <mkoutny@xxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Acked-by: Roman Gushchin <guro@xxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
> Documentation/admin-guide/cgroup-v1/memory.rst | 2 ++
> mm/memcontrol.c | 14 ++++++++++++--
> 2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
> index faac50149a222..2cc502a75ef64 100644
> --- a/Documentation/admin-guide/cgroup-v1/memory.rst
> +++ b/Documentation/admin-guide/cgroup-v1/memory.rst
> @@ -64,6 +64,7 @@ Brief summary of control files.
> threads
> cgroup.procs show list of processes
> cgroup.event_control an interface for event_fd()
> + This knob is not available on CONFIG_PREEMPT_RT systems.
> memory.usage_in_bytes show current usage for memory
> (See 5.5 for details)
> memory.memsw.usage_in_bytes show current usage for memory+Swap
> @@ -75,6 +76,7 @@ Brief summary of control files.
> memory.max_usage_in_bytes show max memory usage recorded
> 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.
> memory.stat show various statistics
> memory.use_hierarchy set/show hierarchical account enabled
> This knob is deprecated and shouldn't be
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 8ab2dc75e70ec..0b5117ed2ae08 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -859,6 +859,9 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
> */
> static void memcg_check_events(struct mem_cgroup *memcg, int nid)
> {
> + if (IS_ENABLED(CONFIG_PREEMPT_RT))
> + return;
> +
> /* threshold event is triggered in finer grain than soft limit */
> if (unlikely(mem_cgroup_event_ratelimit(memcg,
> MEM_CGROUP_TARGET_THRESH))) {
> @@ -3731,8 +3734,12 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
> }
> break;
> case RES_SOFT_LIMIT:
> - memcg->soft_limit = nr_pages;
> - ret = 0;
> + if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
> + ret = -EOPNOTSUPP;
> + } else {
> + memcg->soft_limit = nr_pages;
> + ret = 0;
> + }
> break;
> }
> return ret ?: nbytes;
> @@ -4708,6 +4715,9 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
> char *endp;
> int ret;
>
> + if (IS_ENABLED(CONFIG_PREEMPT_RT))
> + return -EOPNOTSUPP;
> +
> buf = strstrip(buf);
>
> efd = simple_strtoul(buf, &endp, 10);
> --
> 2.34.1
--
Michal Hocko
SUSE Labs
