Date:	Tue, 8 Jul 2014 15:57:34 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	lizefan@...wei.com, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH 3/4] cgroup: remove sane_behavior support on non-default
 hierarchies

On Wed, Jul 02, 2014 at 07:45:46PM -0400, Tejun Heo wrote:
> sane_behavior has been used as a development vehicle for the default
> unified hierarchy.  Now that the default hierarchy is in place, the
> flag became redundant and confusing as its usage is allowed on all
> hierarchies.  There are gonna be either the default hierarchy or
> legacy ones.  Let's make that clear by removing sane_behavior support
> on non-default hierarchies.
> 
> This patch replaces cgroup_sane_behavior() with cgroup_on_dfl().  The
> comment on top of CGRP_ROOT_SANE_BEHAVIOR is moved to on top of
> cgroup_on_dfl() with sane_behavior specific part dropped.
> 
> On the default and legacy hierarchies w/o sane_behavior, this
> shouldn't cause any behavior differences.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.cz>
> ---
>  block/blk-throttle.c   |   6 +--

blk-throttle change looks good to me.

Acked-by: Vivek Goyal <vgoyal@...hat.com>

Vivek

>  include/linux/cgroup.h | 125 +++++++++++++++++++++----------------------------
>  kernel/cgroup.c        |  19 ++++----
>  kernel/cpuset.c        |  33 ++++++-------
>  mm/memcontrol.c        |   7 +--
>  5 files changed, 86 insertions(+), 104 deletions(-)
> 
> diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> index 3fdb21a..9273d09 100644
> --- a/block/blk-throttle.c
> +++ b/block/blk-throttle.c
> @@ -412,13 +412,13 @@ static void throtl_pd_init(struct blkcg_gq *blkg)
>  	int rw;
>  
>  	/*
> -	 * If sane_hierarchy is enabled, we switch to properly hierarchical
> +	 * If on the default hierarchy, we switch to properly hierarchical
>  	 * behavior where limits on a given throtl_grp are applied to the
>  	 * whole subtree rather than just the group itself.  e.g. If 16M
>  	 * read_bps limit is set on the root group, the whole system can't
>  	 * exceed 16M for the device.
>  	 *
> -	 * If sane_hierarchy is not enabled, the broken flat hierarchy
> +	 * If not on the default hierarchy, the broken flat hierarchy
>  	 * behavior is retained where all throtl_grps are treated as if
>  	 * they're all separate root groups right below throtl_data.
>  	 * Limits of a group don't interact with limits of other groups
> @@ -426,7 +426,7 @@ static void throtl_pd_init(struct blkcg_gq *blkg)
>  	 */
>  	parent_sq = &td->service_queue;
>  
> -	if (cgroup_sane_behavior(blkg->blkcg->css.cgroup) && blkg->parent)
> +	if (cgroup_on_dfl(blkg->blkcg->css.cgroup) && blkg->parent)
>  		parent_sq = &blkg_to_tg(blkg->parent)->service_queue;
>  
>  	throtl_service_queue_init(&tg->service_queue, parent_sq);
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 7748e5b..46e4661 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -248,68 +248,7 @@ struct cgroup {
>  
>  /* cgroup_root->flags */
>  enum {
> -	/*
> -	 * Unfortunately, cgroup core and various controllers are riddled
> -	 * with idiosyncrasies and pointless options.  The following flag,
> -	 * when set, will force sane behavior - some options are forced on,
> -	 * others are disallowed, and some controllers will change their
> -	 * hierarchical or other behaviors.
> -	 *
> -	 * The set of behaviors affected by this flag are still being
> -	 * determined and developed and the mount option for this flag is
> -	 * prefixed with __DEVEL__.  The prefix will be dropped once we
> -	 * reach the point where all behaviors are compatible with the
> -	 * planned unified hierarchy, which will automatically turn on this
> -	 * flag.
> -	 *
> -	 * The followings are the behaviors currently affected this flag.
> -	 *
> -	 * - Mount options "noprefix", "xattr", "clone_children",
> -	 *   "release_agent" and "name" are disallowed.
> -	 *
> -	 * - When mounting an existing superblock, mount options should
> -	 *   match.
> -	 *
> -	 * - Remount is disallowed.
> -	 *
> -	 * - rename(2) is disallowed.
> -	 *
> -	 * - "tasks" is removed.  Everything should be at process
> -	 *   granularity.  Use "cgroup.procs" instead.
> -	 *
> -	 * - "cgroup.procs" is not sorted.  pids will be unique unless they
> -	 *   got recycled inbetween reads.
> -	 *
> -	 * - "release_agent" and "notify_on_release" are removed.
> -	 *   Replacement notification mechanism will be implemented.
> -	 *
> -	 * - "cgroup.clone_children" is removed.
> -	 *
> -	 * - "cgroup.subtree_populated" is available.  Its value is 0 if
> -	 *   the cgroup and its descendants contain no task; otherwise, 1.
> -	 *   The file also generates kernfs notification which can be
> -	 *   monitored through poll and [di]notify when the value of the
> -	 *   file changes.
> -	 *
> -	 * - If mount is requested with sane_behavior but without any
> -	 *   subsystem, the default unified hierarchy is mounted.
> -	 *
> -	 * - cpuset: tasks will be kept in empty cpusets when hotplug happens
> -	 *   and take masks of ancestors with non-empty cpus/mems, instead of
> -	 *   being moved to an ancestor.
> -	 *
> -	 * - cpuset: a task can be moved into an empty cpuset, and again it
> -	 *   takes masks of ancestors.
> -	 *
> -	 * - memcg: use_hierarchy is on by default and the cgroup file for
> -	 *   the flag is not created.
> -	 *
> -	 * - blkcg: blk-throttle becomes properly hierarchical.
> -	 *
> -	 * - debug: disallowed on the default hierarchy.
> -	 */
> -	CGRP_ROOT_SANE_BEHAVIOR	= (1 << 0),
> -
> +	CGRP_ROOT_SANE_BEHAVIOR	= (1 << 0), /* __DEVEL__sane_behavior specified */
>  	CGRP_ROOT_NOPREFIX	= (1 << 1), /* mounted subsystems have no named prefix */
>  	CGRP_ROOT_XATTR		= (1 << 2), /* supports extended attributes */
>  };
> @@ -523,20 +462,64 @@ struct cftype {
>  extern struct cgroup_root cgrp_dfl_root;
>  extern struct css_set init_css_set;
>  
> +/**
> + * cgroup_on_dfl - test whether a cgroup is on the default hierarchy
> + * @cgrp: the cgroup of interest
> + *
> + * The default hierarchy is the v2 interface of cgroup and this function
> + * can be used to test whether a cgroup is on the default hierarchy for
> + * cases where a subsystem should behave differnetly depending on the
> + * interface version.
> + *
> + * The set of behaviors which change on the default hierarchy are still
> + * being determined and the mount option is prefixed with __DEVEL__.
> + *
> + * List of changed behaviors:
> + *
> + * - Mount options "noprefix", "xattr", "clone_children", "release_agent"
> + *   and "name" are disallowed.
> + *
> + * - When mounting an existing superblock, mount options should match.
> + *
> + * - Remount is disallowed.
> + *
> + * - rename(2) is disallowed.
> + *
> + * - "tasks" is removed.  Everything should be at process granularity.  Use
> + *   "cgroup.procs" instead.
> + *
> + * - "cgroup.procs" is not sorted.  pids will be unique unless they got
> + *   recycled inbetween reads.
> + *
> + * - "release_agent" and "notify_on_release" are removed.  Replacement
> + *   notification mechanism will be implemented.
> + *
> + * - "cgroup.clone_children" is removed.
> + *
> + * - "cgroup.subtree_populated" is available.  Its value is 0 if the cgroup
> + *   and its descendants contain no task; otherwise, 1.  The file also
> + *   generates kernfs notification which can be monitored through poll and
> + *   [di]notify when the value of the file changes.
> + *
> + * - cpuset: tasks will be kept in empty cpusets when hotplug happens and
> + *   take masks of ancestors with non-empty cpus/mems, instead of being
> + *   moved to an ancestor.
> + *
> + * - cpuset: a task can be moved into an empty cpuset, and again it takes
> + *   masks of ancestors.
> + *
> + * - memcg: use_hierarchy is on by default and the cgroup file for the flag
> + *   is not created.
> + *
> + * - blkcg: blk-throttle becomes properly hierarchical.
> + *
> + * - debug: disallowed on the default hierarchy.
> + */
>  static inline bool cgroup_on_dfl(const struct cgroup *cgrp)
>  {
>  	return cgrp->root == &cgrp_dfl_root;
>  }
>  
> -/*
> - * See the comment above CGRP_ROOT_SANE_BEHAVIOR for details.  This
> - * function can be called as long as @cgrp is accessible.
> - */
> -static inline bool cgroup_sane_behavior(const struct cgroup *cgrp)
> -{
> -	return cgrp->root->flags & CGRP_ROOT_SANE_BEHAVIOR;
> -}
> -
>  /* no synchronization, the result can only be used as a hint */
>  static inline bool cgroup_has_tasks(struct cgroup *cgrp)
>  {
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index be701d9..2d7057e 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1414,8 +1414,8 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
>  	struct cgroup_sb_opts opts;
>  	unsigned int added_mask, removed_mask;
>  
> -	if (root->flags & CGRP_ROOT_SANE_BEHAVIOR) {
> -		pr_err("sane_behavior: remount is not allowed\n");
> +	if (root == &cgrp_dfl_root) {
> +		pr_err("remount is not allowed\n");
>  		return -EINVAL;
>  	}
>  
> @@ -2833,9 +2833,9 @@ static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
>  
>  	/*
>  	 * This isn't a proper migration and its usefulness is very
> -	 * limited.  Disallow if sane_behavior.
> +	 * limited.  Disallow on the default hierarchy.
>  	 */
> -	if (cgroup_sane_behavior(cgrp))
> +	if (cgroup_on_dfl(cgrp))
>  		return -EPERM;
>  
>  	/*
> @@ -2921,7 +2921,7 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[],
>  		/* does cft->flags tell us to skip this file on @cgrp? */
>  		if ((cft->flags & CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp))
>  			continue;
> -		if ((cft->flags & CFTYPE_INSANE) && cgroup_sane_behavior(cgrp))
> +		if ((cft->flags & CFTYPE_INSANE) && cgroup_on_dfl(cgrp))
>  			continue;
>  		if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgroup_parent(cgrp))
>  			continue;
> @@ -3654,8 +3654,9 @@ after:
>   *
>   * All this extra complexity was caused by the original implementation
>   * committing to an entirely unnecessary property.  In the long term, we
> - * want to do away with it.  Explicitly scramble sort order if
> - * sane_behavior so that no such expectation exists in the new interface.
> + * want to do away with it.  Explicitly scramble sort order if on the
> + * default hierarchy so that no such expectation exists in the new
> + * interface.
>   *
>   * Scrambling is done by swapping every two consecutive bits, which is
>   * non-identity one-to-one mapping which disturbs sort order sufficiently.
> @@ -3670,7 +3671,7 @@ static pid_t pid_fry(pid_t pid)
>  
>  static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid)
>  {
> -	if (cgroup_sane_behavior(cgrp))
> +	if (cgroup_on_dfl(cgrp))
>  		return pid_fry(pid);
>  	else
>  		return pid;
> @@ -3773,7 +3774,7 @@ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
>  	css_task_iter_end(&it);
>  	length = n;
>  	/* now sort & (if procs) strip out duplicates */
> -	if (cgroup_sane_behavior(cgrp))
> +	if (cgroup_on_dfl(cgrp))
>  		sort(array, length, sizeof(pid_t), fried_cmppid, NULL);
>  	else
>  		sort(array, length, sizeof(pid_t), cmppid, NULL);
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index f6b33c6..f9d4807 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -1383,12 +1383,9 @@ static int cpuset_can_attach(struct cgroup_subsys_state *css,
>  
>  	mutex_lock(&cpuset_mutex);
>  
> -	/*
> -	 * We allow to move tasks into an empty cpuset if sane_behavior
> -	 * flag is set.
> -	 */
> +	/* allow moving tasks into an empty cpuset if on default hierarchy */
>  	ret = -ENOSPC;
> -	if (!cgroup_sane_behavior(css->cgroup) &&
> +	if (!cgroup_on_dfl(css->cgroup) &&
>  	    (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed)))
>  		goto out_unlock;
>  
> @@ -2030,7 +2027,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs)
>  	static cpumask_t off_cpus;
>  	static nodemask_t off_mems;
>  	bool is_empty;
> -	bool sane = cgroup_sane_behavior(cs->css.cgroup);
> +	bool on_dfl = cgroup_on_dfl(cs->css.cgroup);
>  
>  retry:
>  	wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);
> @@ -2054,12 +2051,12 @@ retry:
>  	mutex_unlock(&callback_mutex);
>  
>  	/*
> -	 * If sane_behavior flag is set, we need to update tasks' cpumask
> -	 * for empty cpuset to take on ancestor's cpumask. Otherwise, don't
> -	 * call update_tasks_cpumask() if the cpuset becomes empty, as
> -	 * the tasks in it will be migrated to an ancestor.
> +	 * If on_dfl, we need to update tasks' cpumask for empty cpuset to
> +	 * take on ancestor's cpumask. Otherwise, don't call
> +	 * update_tasks_cpumask() if the cpuset becomes empty, as the tasks
> +	 * in it will be migrated to an ancestor.
>  	 */
> -	if ((sane && cpumask_empty(cs->cpus_allowed)) ||
> +	if ((on_dfl && cpumask_empty(cs->cpus_allowed)) ||
>  	    (!cpumask_empty(&off_cpus) && !cpumask_empty(cs->cpus_allowed)))
>  		update_tasks_cpumask(cs);
>  
> @@ -2068,12 +2065,12 @@ retry:
>  	mutex_unlock(&callback_mutex);
>  
>  	/*
> -	 * If sane_behavior flag is set, we need to update tasks' nodemask
> -	 * for empty cpuset to take on ancestor's nodemask. Otherwise, don't
> -	 * call update_tasks_nodemask() if the cpuset becomes empty, as
> -	 * the tasks in it will be migratd to an ancestor.
> +	 * If on_dfl, we need to update tasks' nodemask for empty cpuset to
> +	 * take on ancestor's nodemask. Otherwise, don't call
> +	 * update_tasks_nodemask() if the cpuset becomes empty, as the
> +	 * tasks in it will be migratd to an ancestor.
>  	 */
> -	if ((sane && nodes_empty(cs->mems_allowed)) ||
> +	if ((on_dfl && nodes_empty(cs->mems_allowed)) ||
>  	    (!nodes_empty(off_mems) && !nodes_empty(cs->mems_allowed)))
>  		update_tasks_nodemask(cs);
>  
> @@ -2083,13 +2080,13 @@ retry:
>  	mutex_unlock(&cpuset_mutex);
>  
>  	/*
> -	 * If sane_behavior flag is set, we'll keep tasks in empty cpusets.
> +	 * If on_dfl, we'll keep tasks in empty cpusets.
>  	 *
>  	 * Otherwise move tasks to the nearest ancestor with execution
>  	 * resources.  This is full cgroup operation which will
>  	 * also call back into cpuset.  Should be done outside any lock.
>  	 */
> -	if (!sane && is_empty)
> +	if (!on_dfl && is_empty)
>  		remove_tasks_in_empty_cpuset(cs);
>  }
>  
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a2c7bcb..f986671 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -7001,16 +7001,17 @@ static void mem_cgroup_move_task(struct cgroup_subsys_state *css,
>  
>  /*
>   * Cgroup retains root cgroups across [un]mount cycles making it necessary
> - * to verify sane_behavior flag on each mount attempt.
> + * to verify whether we're attached to the default hierarchy on each mount
> + * attempt.
>   */
>  static void mem_cgroup_bind(struct cgroup_subsys_state *root_css)
>  {
>  	/*
> -	 * use_hierarchy is forced with sane_behavior.  cgroup core
> +	 * use_hierarchy is forced on the default hierarchy.  cgroup core
>  	 * guarantees that @root doesn't have any children, so turning it
>  	 * on for the root memcg is enough.
>  	 */
> -	if (cgroup_sane_behavior(root_css->cgroup))
> +	if (cgroup_on_dfl(root_css->cgroup))
>  		mem_cgroup_from_css(root_css)->use_hierarchy = true;
>  }
>  
> -- 
> 1.9.3
> 
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