Re: [PATCH] cgroup: remove extra calls to find_existing_css_set

[Li Zefan <lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>]

Mandeep Singh Baines wrote:
> In cgroup_attach_proc, we indirectly call find_existing_css_set 3
> times. It is an expensive call so we want to call it a minimum
> of times. This patch only calls it once and stores the result so
> that it can be used later on when we call cgroup_task_migrate.
> 
> This required modifying cgroup_task_migrate to take the new css_set
> (which we obtained from find_css_set) as a parameter. The nice side
> effect of this is that cgroup_task_migrate is now identical for
> cgroup_attach_task and cgroup_attach_proc. It also now returns a
> void since it can never fail.
> 
> Changes in V5:
> * https://lkml.org/lkml/2012/1/20/344 (Tejun Heo)
>   * Remove css_set_refs
> Changes in V4:
> * https://lkml.org/lkml/2011/12/22/421 (Li Zefan)
>   * Avoid GFP_KERNEL (sleep) in rcu_read_lock by getting css_set in
>     a separate loop not under an rcu_read_lock
> Changes in V3:
> * https://lkml.org/lkml/2011/12/22/13 (Li Zefan)
>   * Fixed earlier bug by creating a seperate patch to remove tasklist_lock
> Changes in V2:
> * https://lkml.org/lkml/2011/12/20/372 (Tejun Heo)
>   * Move find_css_set call into loop which creates the flex array
> * Author
>   * Kill css_set_refs and use group_size instead
>   * Fix an off-by-one error in counting css_set refs
>   * Add a retval check in out_list_teardown
> 
> Signed-off-by: Mandeep Singh Baines <msb-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>

Please add my ack in your changelog when you update the patch.

> Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Cc: Li Zefan <lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
> Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
> Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> Cc: Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Cc: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
> Cc: Paul Menage <paul-inf54ven1CmVyaH7bEyXVA@public.gmane.org>
> ---
>  kernel/cgroup.c |  143 +++++++++++--------------------------------------------
>  1 files changed, 28 insertions(+), 115 deletions(-)