Re: [PATCHSET] cgroup: introduce cgroup_taskset and consolidate subsys methods

On Wed, Aug 24, 2011 at 12:19:54AM +0200, Tejun Heo wrote:

Hello,

cgroup has grown quite some number of subsys methods.  Some of them
are overlapping, inconsistent with each other and called under
different conditions depending on whether they're called for a single
task or whole process.  Unfortunately, these callbacks are complicated
and incomplete at the same time.

* ->attach_task() is called after migration for task attach but before
  for process.

* Ditto for ->pre_attach().

* ->can_attach_task() is called for every task in the thread group but
  ->attach_task() skips the ones which don't actually change cgroups.

* Task attach becomes noop if the task isn't actually moving.  Process
  attach is always performed.

* ->attach_task() doesn't (or at least aren't supposed to) have access
  to the old cgroup.

* During cancel, there's no way to access the affected tasks.

This patchset introduces cgroup_taskset along with some accessors and
iterator, updates methods to use it, consolidates usages and drops
superflous methods.

It contains the following six patches.

 0001-cgroup-subsys-attach_task-should-be-called-after-mig.patch
 0002-cgroup-improve-old-cgroup-handling-in-cgroup_attach_.patch
 0003-cgroup-introduce-cgroup_taskset-and-use-it-in-subsys.patch
 0004-cgroup-don-t-use-subsys-can_attach_task-or-attach_ta.patch
 0005-cgroup-cpuset-don-t-use-ss-pre_attach.patch
 0006-cgroup-kill-subsys-can_attach_task-pre_attach-and-at.patch

I don't understand the point on patches 3,4,5,6

Why pushing the task iterations down to the subsystems?