A recent commit 9852ae3fe529 ("mm, memcg: consider subtrees in memory.events") changed the behavior of memcg events, which will now consider subtrees in memory.events. But oom_kill event is a special one as it is used in both cgroup1 and cgroup2. In cgroup1, it is displayed in memory.oom_control. The file memory.oom_control is in both root memcg and non root memcg, that is different with memory.event as it only in non-root memcg. That commit is okay for cgroup2, but it is not okay for cgroup1 as it will cause inconsistent behavior between root memcg and non-root memcg. Here's an example on why this behavior is inconsistent in cgroup1. root memcg / memcg foo / memcg bar Suppose there's an oom_kill in memcg bar, then the oon_kill will be root memcg : memory.oom_control(oom_kill) 0 / memcg foo : memory.oom_control(oom_kill) 1 / memcg bar : memory.oom_control(oom_kill) 1 For the non-root memcg, its memory.oom_control(oom_kill) includes its descendants' oom_kill, but for root memcg, it doesn't include its descendants' oom_kill. That means, memory.oom_control(oom_kill) has different meanings in different memcgs. That is inconsistent. Then the user has to know whether the memcg is root or not. If we can't fully support it in cgroup1, for example by adding memory.events.local into cgroup1 as well, then let's don't touch its original behavior.
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| @@ -783,6 +783,8 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg, · 782 unmodified lines | ||
| 783 | 783 | atomic_long_inc(&memcg->memory_events[event]); |
| 784 | 784 | cgroup_file_notify(&memcg->events_file); |
| 785 | 785 | |
| 786 | + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) | |
| 787 | + break; | |
| 786 | 788 | if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS) |
| 787 | 789 | break; |
| 788 | 790 | } while ((memcg = parent_mem_cgroup(memcg)) && |