On 2013/7/12 17:29, Michal Hocko wrote:
> On Fri 12-07-13 17:20:09, Li Zefan wrote:
> [...]
>> But if I read the code correctly, even no one registers a vmpressure event,
>> vmpressure() is always running and queue the work item.
>
> True but checking there is somebody is rather impractical. First we
> would have to take a events_lock to check this and then drop it after
> scheduling the work. Which doesn't guarantee that the registered event
> wouldn't go away.
> And even trickier, we would have to do the same for all parents up the
> hierarchy.
>
The thing is, we can forget about eventfd. eventfd is checked in
vmpressure_work_fn(), while vmpressure() is always called no matter what.
vmpressure()
queue_work()
cgroup_diput()
call_rcu(cgroup_free_rcu)
...
queue_work(destroy_cgroup)
...
cgroup_free_fn()
mem_cgroup_destroy()
...
vmpress_work_fn()
There's no guarantee that vmpressure work is run before cgroup destroy
work, I think.
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