Hello,

On Fri, Feb 03, 2017 at 01:10:21PM -0800, Andy Lutomirski wrote:

Is this flexible enough for the real-world usecases?  For my use case

I can't think of a reason why it won't be.  Capability-wise, nothing
is being lost by the interface.

(if I actually ported over to this), it would mean that I'd have to
enable thread mode on the root.  What about letting a given process
(actually mm, perhaps) live in a cgroup but let the threads be in
different cgroups without any particular constraints.  Then
process-wide stuff would be accounted to the cgroup that owns the
process.

I don't know.  So, then, we basiclly have completely separate trees
for resource domains and threads.  That exactly is what mounting cpu
controller separately does.  It doesn't make sense to put them on the
same hierarchy.  Why?

quoted

If a controller can't possibly define how internal competition should
be handled, which is unlikely - the problem is being consistent and
sensible, defining something isn't difficult - the controller can
simply error out those cases either on configuration or migration.
Again, I'm very doubtful we'll need that but if we ever need that
denying specific configurations is the best we can do anyway.

I'm not sure I follow.

I'm suggesting something quite simple: let controllers that don't need
the no-internal-process constraints set a flag so that the constraints
don't apply if all enabled controllers have the flag set.

Firstly, I think it's better to have the rules as simple and
consistent as possible as long as we don't sacrifice critical
capabilities.

Secondly, all the major resource controllers including cpu would
eventually need resource domain, so there is no real practical upside
to doing so.

Thirdly, if we commit to something like "controller X is not subject
to no-internal-process constraint", that commitment would prevent from
ever adding domain level operations to that controller without
breaking userland visible interface.  All controllers do and have to
support process level operations.  Some controllers can do thread
level operations.  Keeping the latter opt-in doesn't block us from
adding thread mode later on.  Doing it the other way around blocks us
from adding domain level operations later on.

Thanks.

-- 
tejun