Re: [PATCH v2 8/8] cgroup: kill css_id

From: Michal Hocko
Date: Wed Jul 24 2013 - 10:31:17 EST

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On Wed 24-07-13 18:03:36, Li Zefan wrote:
> The only user of css_id was memcg, and it has been convered to use
> cgroup->id, so kill css_id.
>
> Signed-off-by: Li Zefan <lizefan@xxxxxxxxx>

Nice
Reviewed-by: Michal Hocko <mhocko@xxxxxxx>

> ---
> include/linux/cgroup.h | 37 --------
> kernel/cgroup.c | 252 +------------------------------------------------
> 2 files changed, 1 insertion(+), 288 deletions(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index e8eb361..ec8c380 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -599,11 +599,6 @@ struct cgroup_subsys {
> int subsys_id;
> int disabled;
> int early_init;
> - /*
> - * True if this subsys uses ID. ID is not available before cgroup_init()
> - * (not available in early_init time.)
> - */
> - bool use_id;
>
> /*
> * If %false, this subsystem is properly hierarchical -
> @@ -629,9 +624,6 @@ struct cgroup_subsys {
> */
> struct cgroupfs_root *root;
> struct list_head sibling;
> - /* used when use_id == true */
> - struct idr idr;
> - spinlock_t id_lock;
>
> /* list of cftype_sets */
> struct list_head cftsets;
> @@ -858,35 +850,6 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan);
> int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
> int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);
>
> -/*
> - * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works
> - * if cgroup_subsys.use_id == true. It can be used for looking up and scanning.
> - * CSS ID is assigned at cgroup allocation (create) automatically
> - * and removed when subsys calls free_css_id() function. This is because
> - * the lifetime of cgroup_subsys_state is subsys's matter.
> - *
> - * Looking up and scanning function should be called under rcu_read_lock().
> - * Taking cgroup_mutex is not necessary for following calls.
> - * But the css returned by this routine can be "not populated yet" or "being
> - * destroyed". The caller should check css and cgroup's status.
> - */
> -
> -/*
> - * Typically Called at ->destroy(), or somewhere the subsys frees
> - * cgroup_subsys_state.
> - */
> -void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css);
> -
> -/* Find a cgroup_subsys_state which has given ID */
> -
> -struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id);
> -
> -/* Returns true if root is ancestor of cg */
> -bool css_is_ancestor(struct cgroup_subsys_state *cg,
> - const struct cgroup_subsys_state *root);
> -
> -/* Get id and depth of css */
> -unsigned short css_id(struct cgroup_subsys_state *css);
> struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id);
>
> #else /* !CONFIG_CGROUPS */
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 9b27775..4333cb7 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -123,38 +123,6 @@ struct cfent {
> };
>
> /*
> - * CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
> - * cgroup_subsys->use_id != 0.
> - */
> -#define CSS_ID_MAX (65535)
> -struct css_id {
> - /*
> - * The css to which this ID points. This pointer is set to valid value
> - * after cgroup is populated. If cgroup is removed, this will be NULL.
> - * This pointer is expected to be RCU-safe because destroy()
> - * is called after synchronize_rcu(). But for safe use, css_tryget()
> - * should be used for avoiding race.
> - */
> - struct cgroup_subsys_state __rcu *css;
> - /*
> - * ID of this css.
> - */
> - unsigned short id;
> - /*
> - * Depth in hierarchy which this ID belongs to.
> - */
> - unsigned short depth;
> - /*
> - * ID is freed by RCU. (and lookup routine is RCU safe.)
> - */
> - struct rcu_head rcu_head;
> - /*
> - * Hierarchy of CSS ID belongs to.
> - */
> - unsigned short stack[0]; /* Array of Length (depth+1) */
> -};
> -
> -/*
> * cgroup_event represents events which userspace want to receive.
> */
> struct cgroup_event {
> @@ -364,9 +332,6 @@ struct cgrp_cset_link {
> static struct css_set init_css_set;
> static struct cgrp_cset_link init_cgrp_cset_link;
>
> -static int cgroup_init_idr(struct cgroup_subsys *ss,
> - struct cgroup_subsys_state *css);
> -
> /* css_set_lock protects the list of css_set objects, and the
> * chain of tasks off each css_set. Nests outside task->alloc_lock
> * due to cgroup_iter_start() */
> @@ -815,9 +780,6 @@ static struct backing_dev_info cgroup_backing_dev_info = {
> .capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK,
> };
>
> -static int alloc_css_id(struct cgroup_subsys *ss,
> - struct cgroup *parent, struct cgroup *child);
> -
> static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
> {
> struct inode *inode = new_inode(sb);
> @@ -4160,20 +4122,6 @@ static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask)
> }
> }
>
> - /* This cgroup is ready now */
> - for_each_root_subsys(cgrp->root, ss) {
> - struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
> - struct css_id *id = rcu_dereference_protected(css->id, true);
> -
> - /*
> - * Update id->css pointer and make this css visible from
> - * CSS ID functions. This pointer will be dereferened
> - * from RCU-read-side without locks.
> - */
> - if (id)
> - rcu_assign_pointer(id->css, css);
> - }
> -
> return 0;
> err:
> cgroup_clear_dir(cgrp, subsys_mask);
> @@ -4202,7 +4150,6 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
> {
> css->cgroup = cgrp;
> css->flags = 0;
> - css->id = NULL;
> if (cgrp == cgroup_dummy_top)
> css->flags |= CSS_ROOT;
> BUG_ON(cgrp->subsys[ss->subsys_id]);
> @@ -4331,12 +4278,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
> goto err_free_all;
>
> init_cgroup_css(css, ss, cgrp);
> -
> - if (ss->use_id) {
> - err = alloc_css_id(ss, parent, cgrp);
> - if (err)
> - goto err_free_all;
> - }
> }
>
> /*
> @@ -4741,12 +4682,6 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
>
> /* our new subsystem will be attached to the dummy hierarchy. */
> init_cgroup_css(css, ss, cgroup_dummy_top);
> - /* init_idr must be after init_cgroup_css because it sets css->id. */
> - if (ss->use_id) {
> - ret = cgroup_init_idr(ss, css);
> - if (ret)
> - goto err_unload;
> - }
>
> /*
> * Now we need to entangle the css into the existing css_sets. unlike
> @@ -4812,9 +4747,6 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
>
> offline_css(ss, cgroup_dummy_top);
>
> - if (ss->use_id)
> - idr_destroy(&ss->idr);
> -
> /* deassign the subsys_id */
> cgroup_subsys[ss->subsys_id] = NULL;
>
> @@ -4841,8 +4773,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
> /*
> * remove subsystem's css from the cgroup_dummy_top and free it -
> * need to free before marking as null because ss->css_free needs
> - * the cgrp->subsys pointer to find their state. note that this
> - * also takes care of freeing the css_id.
> + * the cgrp->subsys pointer to find their state.
> */
> ss->css_free(cgroup_dummy_top);
> cgroup_dummy_top->subsys[ss->subsys_id] = NULL;
> @@ -4913,8 +4844,6 @@ int __init cgroup_init(void)
> for_each_builtin_subsys(ss, i) {
> if (!ss->early_init)
> cgroup_init_subsys(ss);
> - if (ss->use_id)
> - cgroup_init_idr(ss, init_css_set.subsys[ss->subsys_id]);
> }
>
> /* allocate id for the dummy hierarchy */
> @@ -5335,185 +5264,6 @@ static int __init cgroup_disable(char *str)
> __setup("cgroup_disable=", cgroup_disable);
>
> /*
> - * Functons for CSS ID.
> - */
> -
> -/* to get ID other than 0, this should be called when !cgroup_is_dead() */
> -unsigned short css_id(struct cgroup_subsys_state *css)
> -{
> - struct css_id *cssid;
> -
> - /*
> - * This css_id() can return correct value when somone has refcnt
> - * on this or this is under rcu_read_lock(). Once css->id is allocated,
> - * it's unchanged until freed.
> - */
> - cssid = rcu_dereference_raw(css->id);
> -
> - if (cssid)
> - return cssid->id;
> - return 0;
> -}
> -EXPORT_SYMBOL_GPL(css_id);
> -
> -/**
> - * css_is_ancestor - test "root" css is an ancestor of "child"
> - * @child: the css to be tested.
> - * @root: the css supporsed to be an ancestor of the child.
> - *
> - * Returns true if "root" is an ancestor of "child" in its hierarchy. Because
> - * this function reads css->id, the caller must hold rcu_read_lock().
> - * But, considering usual usage, the csses should be valid objects after test.
> - * Assuming that the caller will do some action to the child if this returns
> - * returns true, the caller must take "child";s reference count.
> - * If "child" is valid object and this returns true, "root" is valid, too.
> - */
> -
> -bool css_is_ancestor(struct cgroup_subsys_state *child,
> - const struct cgroup_subsys_state *root)
> -{
> - struct css_id *child_id;
> - struct css_id *root_id;
> -
> - child_id = rcu_dereference(child->id);
> - if (!child_id)
> - return false;
> - root_id = rcu_dereference(root->id);
> - if (!root_id)
> - return false;
> - if (child_id->depth < root_id->depth)
> - return false;
> - if (child_id->stack[root_id->depth] != root_id->id)
> - return false;
> - return true;
> -}
> -
> -void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
> -{
> - struct css_id *id = rcu_dereference_protected(css->id, true);
> -
> - /* When this is called before css_id initialization, id can be NULL */
> - if (!id)
> - return;
> -
> - BUG_ON(!ss->use_id);
> -
> - rcu_assign_pointer(id->css, NULL);
> - rcu_assign_pointer(css->id, NULL);
> - spin_lock(&ss->id_lock);
> - idr_remove(&ss->idr, id->id);
> - spin_unlock(&ss->id_lock);
> - kfree_rcu(id, rcu_head);
> -}
> -EXPORT_SYMBOL_GPL(free_css_id);
> -
> -/*
> - * This is called by init or create(). Then, calls to this function are
> - * always serialized (By cgroup_mutex() at create()).
> - */
> -
> -static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
> -{
> - struct css_id *newid;
> - int ret, size;
> -
> - BUG_ON(!ss->use_id);
> -
> - size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
> - newid = kzalloc(size, GFP_KERNEL);
> - if (!newid)
> - return ERR_PTR(-ENOMEM);
> -
> - idr_preload(GFP_KERNEL);
> - spin_lock(&ss->id_lock);
> - /* Don't use 0. allocates an ID of 1-65535 */
> - ret = idr_alloc(&ss->idr, newid, 1, CSS_ID_MAX + 1, GFP_NOWAIT);
> - spin_unlock(&ss->id_lock);
> - idr_preload_end();
> -
> - /* Returns error when there are no free spaces for new ID.*/
> - if (ret < 0)
> - goto err_out;
> -
> - newid->id = ret;
> - newid->depth = depth;
> - return newid;
> -err_out:
> - kfree(newid);
> - return ERR_PTR(ret);
> -
> -}
> -
> -static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
> - struct cgroup_subsys_state *rootcss)
> -{
> - struct css_id *newid;
> -
> - spin_lock_init(&ss->id_lock);
> - idr_init(&ss->idr);
> -
> - newid = get_new_cssid(ss, 0);
> - if (IS_ERR(newid))
> - return PTR_ERR(newid);
> -
> - newid->stack[0] = newid->id;
> - RCU_INIT_POINTER(newid->css, rootcss);
> - RCU_INIT_POINTER(rootcss->id, newid);
> - return 0;
> -}
> -
> -static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
> - struct cgroup *child)
> -{
> - int subsys_id, i, depth = 0;
> - struct cgroup_subsys_state *parent_css, *child_css;
> - struct css_id *child_id, *parent_id;
> -
> - subsys_id = ss->subsys_id;
> - parent_css = parent->subsys[subsys_id];
> - child_css = child->subsys[subsys_id];
> - parent_id = rcu_dereference_protected(parent_css->id, true);
> - depth = parent_id->depth + 1;
> -
> - child_id = get_new_cssid(ss, depth);
> - if (IS_ERR(child_id))
> - return PTR_ERR(child_id);
> -
> - for (i = 0; i < depth; i++)
> - child_id->stack[i] = parent_id->stack[i];
> - child_id->stack[depth] = child_id->id;
> - /*
> - * child_id->css pointer will be set after this cgroup is available
> - * see cgroup_populate_dir()
> - */
> - rcu_assign_pointer(child_css->id, child_id);
> -
> - return 0;
> -}
> -
> -/**
> - * css_lookup - lookup css by id
> - * @ss: cgroup subsys to be looked into.
> - * @id: the id
> - *
> - * Returns pointer to cgroup_subsys_state if there is valid one with id.
> - * NULL if not. Should be called under rcu_read_lock()
> - */
> -struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
> -{
> - struct css_id *cssid = NULL;
> -
> - BUG_ON(!ss->use_id);
> - cssid = idr_find(&ss->idr, id);
> -
> - if (unlikely(!cssid))
> - return NULL;
> -
> - return rcu_dereference(cssid->css);
> -}
> -EXPORT_SYMBOL_GPL(css_lookup);
> -
> -/*
> * get corresponding css from file open on cgroupfs directory
> */
> struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
> --
> 1.8.0.2
>
> --
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--
Michal Hocko
SUSE Labs
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Next message: Nathan Zimmer: "[PATCH] timer_list: Correct the iterator for timer_list"
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In reply to: Li Zefan: "[PATCH v2 8/8] cgroup: kill css_id"
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