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

[Kirill Tkhai]

On 17.04.2020 15:11, Valeriy Vdovin wrote:
>>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.

(Please, avoid top-posting in your replies. Top-posting is not welcomed. See in Documentation/development-process/2.Process)

Then, we should add a comment about that this is optimization, I think.

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> *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);
>>  
>>        /*
>> 
>