On Fri, Aug 26, 2011 at 12:43:09AM +0200, Tejun Heo wrote:
> Currently, there's no way to pass multiple tasks to cgroup_subsys
> methods necessitating the need for separate per-process and per-task
> methods. This patch introduces cgroup_taskset which can be used to
> pass multiple tasks and their associated cgroups to cgroup_subsys
> methods.
This will be the third iterator-ish pattern in the cgroup code.
It's not your fault but it does seem a bit much to have:
1) When we need to iterate over all tasks in the cgroup and
don't mind holding the css set lock:
void cgroup_iter_start(cgroup, iterator)
task cgroup_iter_next(cgroup, iterator)
void cgroup_iter_end(cgroup, iterator)
2) For subsystem methods when we're iterating over a subset of
tasks that may or may not be in the cgroup (e.g. for can_attach)
-- use cgroup_tasksets:
task cgroup_taskset_first(tset)
task cgroup_taskset_next(tset)
3) An iterator over all the tasks which doesn't hold the css set
lock:
struct cgroup_scanner {
struct cgroup *cg;
int (*test_task)(struct task_struct *p,
struct cgroup_scanner *scan);
void (*process_task)(struct task_struct *p,
struct cgroup_scanner *scan);
struct ptr_heap *heap;
void *data;
};
This is only used in cpuset code so far. Are other cgroup
patches planning on making use of it?
Is there a sane way to merge all this?
Perhaps we could drop the iterator interfaces in 1) and 2) and replace
it with:
tset cgroup_taskset_from_cgroup(cgroup)
which would grab the css set lock to construct the tset from the given
cgroup -- essentially inlining the current iterator code into a single
function.
Of course this would eliminate the restriction that all the tasks in the
taskset are part of the same thread group; that would only be true for
those passed as parameters to the subsystem methods.
Cheers,
-Matt Helsley
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