[Devel] [PATCH v10 6/9] ve/cgroup: unmark ve-root cgroups at container stop

[Valeriy Vdovin]

>Will the function work correctly in case jf we completely remove above "if"? Is this "if" optimization for init_css_set?

This is indeed an optimization. And also it looks like it's the most common case.

________________________________
From: Kirill Tkhai <ktkhai at virtuozzo.com>
Sent: Friday, April 17, 2020 12:15 PM
To: Valeriy Vdovin <Valeriy.Vdovin at virtuozzo.com>; devel at openvz.org <devel at openvz.org>; Konstantin Khorenko <khorenko at virtuozzo.com>; Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
Subject: Re: [PATCH v10 6/9] ve/cgroup: unmark ve-root cgroups at container stop

On 16.04.2020 19:14, Valeriy Vdovin wrote:
> Signed-off-by: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
> Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  include/linux/cgroup.h |  1 +
>  kernel/cgroup.c        | 42 ++++++++++++++++++++++++++++++++++++++++++
>  kernel/ve/ve.c         |  2 ++
>  3 files changed, 45 insertions(+)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 0a42f93..1bd0fe7 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -636,6 +636,7 @@ int cgroup_task_count(const struct cgroup *cgrp);
>
>  #ifdef CONFIG_VE
>  void cgroup_mark_ve_roots(struct ve_struct *ve);
> +void cgroup_unmark_ve_roots(struct ve_struct *ve);
>  #endif
>
>  /*
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 60a4ca4..1dd36ed 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -635,6 +635,35 @@ static struct css_set *find_css_set(
>  }
>
>  /*
> + * Walk each cgroup link of a given css_set and find a cgroup that
> + * is the child of cgroupfs_root in argument.
> + */
> +static struct cgroup *css_cgroup_from_root(struct css_set *css_set,
> +                                         struct cgroupfs_root *root)
> +{
> +     struct cgroup *res = NULL;
> +
> +     BUG_ON(!mutex_is_locked(&cgroup_mutex));
> +     read_lock(&css_set_lock);
> +
> +     if (css_set == &init_css_set) {
> +             res = &root->top_cgroup;

Will the function work correctly in case jf we completely remove above "if"?
Is this "if" optimization for init_css_set?

> +     } else {
> +             struct cg_cgroup_link *link;
> +             list_for_each_entry(link, &css_set->cg_links, cg_link_list) {
> +                     struct cgroup *c = link->cgrp;
> +                     if (c->root == root) {
> +                             res = c;
> +                             break;
> +                     }
> +             }
> +     }
> +     read_unlock(&css_set_lock);
> +     BUG_ON(!res);
> +     return res;
> +}
> +
> +/*
>   * Return the cgroup for "task" from the given hierarchy. Must be
>   * called with cgroup_mutex held.
>   */
> @@ -4237,6 +4266,19 @@ void cgroup_mark_ve_roots(struct ve_struct *ve)
>        mutex_unlock(&cgroup_mutex);
>  }
>
> +void cgroup_unmark_ve_roots(struct ve_struct *ve)
> +{
> +     struct cgroup *cgrp;
> +     struct cgroupfs_root *root;
> +
> +     mutex_lock(&cgroup_mutex);
> +     for_each_active_root(root) {
> +             cgrp = css_cgroup_from_root(ve->root_css_set, root);
> +             clear_bit(CGRP_VE_ROOT, &cgrp->flags);
> +     }
> +     mutex_unlock(&cgroup_mutex);
> +}
> +
>  struct cgroup *cgroup_get_ve_root(struct cgroup *cgrp)
>  {
>        struct cgroup *ve_root = NULL;
> diff --git a/kernel/ve/ve.c b/kernel/ve/ve.c
> index eedb85d..db3b600 100644
> --- a/kernel/ve/ve.c
> +++ b/kernel/ve/ve.c
> @@ -618,6 +618,8 @@ void ve_exit_ns(struct pid_namespace *pid_ns)
>        if (!ve->ve_ns || ve->ve_ns->pid_ns != pid_ns)
>                return;
>
> +     cgroup_unmark_ve_roots(ve);
> +
>        ve_workqueue_stop(ve);
>
>        /*
>

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