Messages in this thread | | | Date | Wed, 30 Oct 2019 17:47:43 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] locking/percpu_rwsem: Rewrite to not use rwsem |
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On Wed, Oct 30, 2019 at 04:57:20PM +0100, Oleg Nesterov wrote: > On 10/29, Peter Zijlstra wrote: > > > > That said, I think cgroups use a variant of percpu-rwsem that wreck rss > > on purpose and always take the slowpaths. > > I forgot (never understodd) why does Android need this. > > I am wondering if it makes any sense to add a config/boot or even runtime > knob for cgroup_threadgroup_rwsem.
It isn't just Android, but Android in specific likes to move tasks between cgroups a lot.
And moving tasks between cgroups is what requires the write-side of the cgroup percpu-rwsem to be taken. Adding an RCU-GP to every task movement wasn't making them happy (which I can understand).
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