Hello, Waiman.
On Fri, Jul 21, 2017 at 04:34:50PM -0400, Waiman Long wrote:
> When thread mode is used, it is possible that some cgroups may be
> in an invalid state. Currently users may not be aware that they are
> invalid until they try to migrate tasks over. This patch disallows
> child cgroup creation on invalid domain. This adds one more failure
> point in reminding users that they are dealing with invalid domains.
> It also minimizes the number of invalid domains outstanding as much
> as possible.
It's a bit inconsistent because we can reach the same forbidden state
by turning a sibling cgroup threaded. Please consider the following.
A
/ \
B C
\
D
Let's say all are domains and we make B threaded. A becomes the
threaded domain, C and D become invalid, which is the configuration
you're trying to prevent. We can either enabling threaded on B too or
relax type modifications further so that people can make C threaded
which makes sense given that that would lead to a topology which has
to supported anyway (if C were threaded before D was created, it'd
look the same).
So, I'm leaning more towards relaxing restrictions and tightening it,
and given that we have to expose invalid state anyway, I think there's
actual benefit in doing so as it gives more flexibility while building
the hierarchy.
Thanks.
--
tejun
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