linux-kernel - Re: [PATCHSET] kernfs, cgroup: reimplement "cgroup.procs" reading for v2

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Date:   Mon, 26 Dec 2016 14:22:18 +0800
From:   Zefan Li <lizefan@...wei.com>
To:     Tejun Heo <tj@...nel.org>, <gregkh@...uxfoundation.org>,
        <hannes@...xchg.org>
CC:     <linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
        <kernel-team@...com>
Subject: Re: [PATCHSET] kernfs, cgroup: reimplement "cgroup.procs" reading for
 v2

On 2016/12/21 0:12, Tejun Heo wrote:
> On cgroup v1, the pid listings in "cgroup.procs" and "tasks" are
> sorted which adds a lot of complications and overhead.  v2 doesn't
> have such requirement and has been intentionally using a modified
> sorting order so that the output doesn't look sorted to users.
> 
> This patchset re-implements "cgroup.procs" reading for v2 which simply
> keeps a css_task_iter open while the file is being read.  Keeping the
> iterator open makes it unnecessary to skip to the right position on
> each read segment and associated errors - e.g. incorrectly skipping
> over pids because earlier pids disappeared between the reads.
> 
> Using persistent iterator across multiple read calls requires
> ->release() callback to clean it up.  kernfs operations
> ->open/release() are added and piped through cftype.
> 
> This patchset contains the following five patches.
> 
>  0001-kernfs-make-kernfs_open_file-mmapped-a-bitfield.patch
>  0002-kernfs-add-kernfs_ops-open-release-callbacks.patch
>  0003-cgroup-add-cftype-open-release-callbacks.patch
>  0004-cgroup-reimplement-reading-cgroup.procs-on-cgroup-v2.patch
>  0005-cgroup-remove-cgroup_pid_fry-and-friends.patch
> 
> 0001 is a misc kernfs patch and 0002 adds ->open/release() to kernfs.
> 0003 pipes ->open/release() through cftype.  0004 implements the new
> cgroup.procs for v2 and 0005 removes the now unused sort order frying
> logic.
> 
> Greg, would it be okay to route the kernfs patches through
> cgroup/for-4.11?
> 
> The patches are also available in the following git branch.
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-cgroup2-procs
> 
> diffstat follows.  Thanks.
> 
>  fs/kernfs/dir.c             |    2 
>  fs/kernfs/file.c            |   53 +++++++++++++++--
>  fs/kernfs/kernfs-internal.h |    2 
>  include/linux/cgroup-defs.h |    3 +
>  include/linux/kernfs.h      |   12 +++-
>  kernel/cgroup.c             |  130 +++++++++++++++++++++++++++++---------------
>  6 files changed, 148 insertions(+), 54 deletions(-)
> 

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