Re: [PATCHSET cgroup/for-3.16] cgroup: iterate cgroup_subsys_states directly

[Li Zefan <lizefan@huawei.com>]

On 2014/5/10 5:31, Tejun Heo wrote:
> Hello,
> 
> Currently, while csses (cgroup_subsys_states) have ->parent linkage
> too, only cgroups form full tree through their ->children and
> ->sibling fields and css iterations naturally is implemented by
> iterating cgroups and then dereferencing the css for the specified
> subsystem.
> 
> There are now use cases where controllers need to iterate through
> csses regardless of their online state as long as they have positive
> reference.  This can't easily be achieved by iterating cgroups because
> its css pointer array needs to be cleared on offline and there may be
> multiple dying csses for a cgroup for the same subsystem and there's
> only one pointer per cgroup-subsystem pair.
> 
> This patchset moves ->children and ->sibling from cgroup to css and
> link all csses in proper trees and then make css iterators walk csses
> directly instead of going through cgroups.  This achieves iteration of
> all non-released csses while also simplifying the iteration
> implementation.  This is also in line with the general direction of
> using csses as the primary structural component.
> 
> This patchset contains the following fourteen patches.
> 
>  0001-cgroup-remove-css_parent.patch
>  0002-cgroup-remove-pointless-has-tasks-children-test-from.patch
>  0003-memcg-update-memcg_has_children-to-use-css_next_chil.patch
>  0004-device_cgroup-remove-direct-access-to-cgroup-childre.patch
>  0005-cgroup-remove-cgroup-parent.patch
>  0006-cgroup-move-cgroup-sibling-and-children-into-cgroup_.patch
>  0007-cgroup-link-all-cgroup_subsys_states-in-their-siblin.patch
>  0008-cgroup-move-cgroup-serial_nr-into-cgroup_subsys_stat.patch
>  0009-cgroup-introduce-CSS_RELEASED-and-reduce-css-iterati.patch
>  0010-cgroup-iterate-cgroup_subsys_states-directly.patch
>  0011-cgroup-use-CSS_ONLINE-instead-of-CGRP_DEAD.patch
>  0012-cgroup-convert-cgroup_has_live_children-into-css_has.patch
>  0013-device_cgroup-use-css_has_online_children-instead-of.patch
>  0014-cgroup-implement-css_tryget.patch
> 
> 0001-0004 are prep patches.
> 
> 0005-0008 move fields from cgroup to css and link csses in tree
> structure instead of cgroups.
> 
> 0009-0010 implement direct css iteration.
> 
> 0011-0013 convert a cgroup based interface to a css one, which is now
> possible as both are the same in terms of the tree structure, and fix
> devcg brekage using it.
> 
> 0014 implements css_tryget() which is to be used to gain access to
> offline but not-yet-released csses.
> 
> This pachset is on top of
> 
>  b9a63d0116e8 ("Merge branch 'for-3.16' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu into for-3.16")
>  + [1] [PATCHSET v2 cgroup/for-3.16] cgroup: post unified hierarchy fixes and updates
>  + [2] (REFRESHED) [PATCHSET cgroup/for-3.16] cgroup: implement cftype->write()
>  + [3] (REFRESHED) [PATCHSET cgroup/for-3.16] cgroup: remove cgroup_tree_mutex
>  + [4] [PATCHSET cgroup/for-3.16] cgroup: use css->refcnt for cgroup reference counting
> 
> and available in the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-direct-css-iteration
> 
> diffstat follows.  Thanks.
> 
>  block/blk-cgroup.h           |    2 
>  include/linux/cgroup.h       |  122 +++++++++++---------
>  kernel/cgroup.c              |  257 ++++++++++++++++++++++++-------------------
>  kernel/cgroup_freezer.c      |    2 
>  kernel/cpuset.c              |    2 
>  kernel/sched/core.c          |    2 
>  kernel/sched/cpuacct.c       |    2 
>  mm/hugetlb_cgroup.c          |    2 
>  mm/memcontrol.c              |   45 +++----
>  net/core/netclassid_cgroup.c |    2 
>  net/core/netprio_cgroup.c    |    2 
>  security/device_cgroup.c     |   17 --
>  12 files changed, 251 insertions(+), 206 deletions(-)
> 

Acked-by: Li Zefan <lizefan@huawei.com>