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mm/memcg: disable threshold event handlers on PREEMPT_RT
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. Link: https://lkml.kernel.org/r/20220226204144.1008339-3-bigeasy@linutronix.de Suggested-by: Michal Hocko <mhocko@kernel.org> Suggested-by: Michal Koutný <mkoutny@suse.com> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Roman Gushchin <guro@fb.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Shakeel Butt <shakeelb@google.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: kernel test robot <oliver.sang@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Cc: Waiman Long <longman@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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2 changed files with 14 additions and 2 deletions
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@ -64,6 +64,7 @@ Brief summary of control files.
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threads
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cgroup.procs show list of processes
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cgroup.event_control an interface for event_fd()
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This knob is not available on CONFIG_PREEMPT_RT systems.
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memory.usage_in_bytes show current usage for memory
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(See 5.5 for details)
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memory.memsw.usage_in_bytes show current usage for memory+Swap
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@ -75,6 +76,7 @@ Brief summary of control files.
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memory.max_usage_in_bytes show max memory usage recorded
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memory.memsw.max_usage_in_bytes show max memory+Swap usage recorded
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memory.soft_limit_in_bytes set/show soft limit of memory usage
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This knob is not available on CONFIG_PREEMPT_RT systems.
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memory.stat show various statistics
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memory.use_hierarchy set/show hierarchical account enabled
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This knob is deprecated and shouldn't be
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@ -858,6 +858,9 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
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*/
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static void memcg_check_events(struct mem_cgroup *memcg, int nid)
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{
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if (IS_ENABLED(CONFIG_PREEMPT_RT))
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return;
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/* threshold event is triggered in finer grain than soft limit */
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if (unlikely(mem_cgroup_event_ratelimit(memcg,
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MEM_CGROUP_TARGET_THRESH))) {
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@ -3731,8 +3734,12 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
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}
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break;
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case RES_SOFT_LIMIT:
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memcg->soft_limit = nr_pages;
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ret = 0;
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if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
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ret = -EOPNOTSUPP;
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} else {
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memcg->soft_limit = nr_pages;
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ret = 0;
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}
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break;
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}
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return ret ?: nbytes;
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@ -4708,6 +4715,9 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
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char *endp;
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int ret;
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if (IS_ENABLED(CONFIG_PREEMPT_RT))
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return -EOPNOTSUPP;
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buf = strstrip(buf);
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efd = simple_strtoul(buf, &endp, 10);
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