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SubjectRe: [PATCH v2 08/23] cgroup: pass around cgroup_subsys_state instead of cgroup in subsystem methods
On 08/02/2013 10:24 PM, Tejun Heo wrote:
> cgroup is currently in the process of transitioning to using struct
> cgroup_subsys_state * as the primary handle instead of struct cgroup *
> in subsystem implementations for the following reasons.
>
> * With unified hierarchy, subsystems will be dynamically bound and
> unbound from cgroups and thus css's (cgroup_subsys_state) may be
> created and destroyed dynamically over the lifetime of a cgroup,
> which is different from the current state where all css's are
> allocated and destroyed together with the associated cgroup. This
> in turn means that cgroup_css() should be synchronized and may
> return NULL, making it more cumbersome to use.
>
> * Differing levels of per-subsystem granularity in the unified
> hierarchy means that the task and descendant iterators should behave
> differently depending on the specific subsystem the iteration is
> being performed for.
>
> * In majority of the cases, subsystems only care about its part in the
> cgroup hierarchy - ie. the hierarchy of css's. Subsystem methods
> often obtain the matching css pointer from the cgroup and don't
> bother with the cgroup pointer itself. Passing around css fits
> much better.
>
> This patch converts all cgroup_subsys methods to take @css instead of
> @cgroup. The conversions are mostly straight-forward. A few
> noteworthy changes are
>
> * ->css_alloc() now takes css of the parent cgroup rather than the
> pointer to the new cgroup as the css for the new cgroup doesn't
> exist yet. Knowing the parent css is enough for all the existing
> subsystems.
>
> * In kernel/cgroup.c::offline_css(), unnecessary open coded css
> dereference is replaced with local variable access.
>
> This patch shouldn't cause any behavior differences.
>
> v2: Unnecessary explicit cgrp->subsys[] deref in css_online() replaced
> with local variable @css as suggested by Li Zefan.
>
> Rebased on top of new for-3.12 which includes for-3.11-fixes so
> that ->css_free() invocation added by da0a12caff ("cgroup: fix a
> leak when percpu_ref_init() fails") is converted too. Suggested
> by Li Zefan.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Acked-by: Li Zefan <lizefan@huawei.com>
> Acked-by: Michal Hocko <mhocko@suse.cz>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Balbir Singh <bsingharora@gmail.com>
> Cc: Aristeu Rozanski <aris@redhat.com>
> Cc: Matt Helsley <matthltc@us.ibm.com>
> Cc: Daniel Wagner <daniel.wagner@bmw-carit.de>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Steven Rostedt <rostedt@goodmis.org>

netprio and cls part:

Acked-By: Daniel Wagner <daniel.wagner@bmw-carit.de>

cheers,
daniel





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