On Tue, Aug 31, 2010 at 11:41 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>
> Now, css'id is allocated after ->create() is called. But to make use of ID
> in ->create(), it should be available before ->create().
>
> In another thinking, considering the ID is tightly coupled with "css",
> it should be allocated when "css" is allocated.
> This patch moves alloc_css_id() to css allocation routine. Now, only 2 subsys,
> memory and blkio are using ID. (To support complicated hierarchy walk.)
>
> ID will be used in mem cgroup's ->create(), later.
>
> This patch adds css ID documentation which is not provided.
>
> Note:
> If someone changes rules of css allocation, ID allocation should be changed.
>
> Changelog: 2010/09/01
> - modified cgroups.txt
>
> Reviewed-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> Acked-by: Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> Documentation/cgroups/cgroups.txt | 48 ++++++++++++++++++++++++++++++++++++
> block/blk-cgroup.c | 9 ++++++
> include/linux/cgroup.h | 16 ++++++------
> kernel/cgroup.c | 50 +++++++++++---------------------------
> mm/memcontrol.c | 5 +++
> 5 files changed, 86 insertions(+), 42 deletions(-)
>
> Index: mmotm-0827/kernel/cgroup.c
> ===================================================================
> --- mmotm-0827.orig/kernel/cgroup.c
> +++ mmotm-0827/kernel/cgroup.c
> @@ -289,9 +289,6 @@ struct cg_cgroup_link {
> static struct css_set init_css_set;
> static struct cg_cgroup_link init_css_set_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() */
> @@ -770,9 +767,6 @@ static struct backing_dev_info cgroup_ba
> .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(mode_t mode, struct super_block *sb)
> {
> struct inode *inode = new_inode(sb);
> @@ -3258,7 +3252,8 @@ static void init_cgroup_css(struct cgrou
> css->cgroup = cgrp;
> atomic_set(&css->refcnt, 1);
> css->flags = 0;
> - css->id = NULL;
> + if (!ss->use_id)
> + css->id = NULL;
> if (cgrp == dummytop)
> set_bit(CSS_ROOT, &css->flags);
> BUG_ON(cgrp->subsys[ss->subsys_id]);
> @@ -3343,12 +3338,6 @@ static long cgroup_create(struct cgroup
> goto err_destroy;
> }
> init_cgroup_css(css, ss, cgrp);
> - if (ss->use_id) {
> - err = alloc_css_id(ss, parent, cgrp);
> - if (err)
> - goto err_destroy;
> - }
> - /* At error, ->destroy() callback has to free assigned ID. */
> }
>
> cgroup_lock_hierarchy(root);
> @@ -3710,17 +3699,6 @@ int __init_or_module cgroup_load_subsys(
>
> /* our new subsystem will be attached to the dummy hierarchy. */
> init_cgroup_css(css, ss, dummytop);
> - /* init_idr must be after init_cgroup_css because it sets css->id. */
> - if (ss->use_id) {
> - int ret = cgroup_init_idr(ss, css);
> - if (ret) {
> - dummytop->subsys[ss->subsys_id] = NULL;
> - ss->destroy(ss, dummytop);
> - subsys[i] = NULL;
> - mutex_unlock(&cgroup_mutex);
> - return ret;
> - }
> - }
>
> /*
> * Now we need to entangle the css into the existing css_sets. unlike
> @@ -3889,8 +3867,6 @@ int __init cgroup_init(void)
> struct cgroup_subsys *ss = subsys[i];
> if (!ss->early_init)
> cgroup_init_subsys(ss);
> - if (ss->use_id)
> - cgroup_init_idr(ss, init_css_set.subsys[ss->subsys_id]);
> }
>
> /* Add init_css_set to the hash table */
> @@ -4604,8 +4580,8 @@ err_out:
>
> }
>
> -static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
> - struct cgroup_subsys_state *rootcss)
> +static int cgroup_init_idr(struct cgroup_subsys *ss,
> + struct cgroup_subsys_state *rootcss)
> {
> struct css_id *newid;
>
> @@ -4617,21 +4593,25 @@ static int __init_or_module cgroup_init_
> return PTR_ERR(newid);
>
> newid->stack[0] = newid->id;
> - newid->css = rootcss;
> - rootcss->id = newid;
> + rcu_assign_pointer(newid->css, rootcss);
> + rcu_assign_pointer(rootcss->id, newid);
> return 0;
> }
>
> -static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
> - struct cgroup *child)
> +int alloc_css_id(struct cgroup_subsys *ss,
> + struct cgroup *cgrp, struct cgroup_subsys_state *css)
Must also add EXPORT_SYMBOL_GPL(alloc_css_id) to supported CONFIG_BLK_CGROUP=m.
> {
> int subsys_id, i, depth = 0;
> - struct cgroup_subsys_state *parent_css, *child_css;
> + struct cgroup_subsys_state *parent_css;
> + struct cgroup *parent;
> struct css_id *child_id, *parent_id;
>
> + if (cgrp == dummytop)
> + return cgroup_init_idr(ss, css);
> +
> + parent = cgrp->parent;
> subsys_id = ss->subsys_id;
> parent_css = parent->subsys[subsys_id];
> - child_css = child->subsys[subsys_id];
> parent_id = parent_css->id;
> depth = parent_id->depth + 1;
>
> @@ -4646,7 +4626,7 @@ static int alloc_css_id(struct cgroup_su
> * child_id->css pointer will be set after this cgroup is available
> * see cgroup_populate_dir()
> */
> - rcu_assign_pointer(child_css->id, child_id);
> + rcu_assign_pointer(css->id, child_id);
>
> return 0;
> }
> Index: mmotm-0827/include/linux/cgroup.h
> ===================================================================
> --- mmotm-0827.orig/include/linux/cgroup.h
> +++ mmotm-0827/include/linux/cgroup.h
> @@ -588,9 +588,11 @@ static inline int cgroup_attach_task_cur
> /*
> * 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.
> + * CSS ID must be assigned by subsys itself at cgroup creation and deleted
> + * when subsys calls free_css_id() function. This is because the life time of
To be consistent with document: s/life time/lifetime/
> + * of cgroup_subsys_state is subsys's matter.
> + *
> + * ID->css look up is available after cgroup's directory is populated.
> *
> * Looking up and scanning function should be called under rcu_read_lock().
> * Taking cgroup_mutex()/hierarchy_mutex() is not necessary for following calls.
> @@ -598,10 +600,10 @@ static inline int cgroup_attach_task_cur
> * destroyed". The caller should check css and cgroup's status.
> */
>
> -/*
> - * Typically Called at ->destroy(), or somewhere the subsys frees
> - * cgroup_subsys_state.
> - */
> +/* Should be called in ->create() by subsys itself */
> +int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *newgr,
> + struct cgroup_subsys_state *css);
> +/* Typically Called at ->destroy(), or somewhere the subsys frees css */
s/Called/called/
> void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css);
>
> /* Find a cgroup_subsys_state which has given ID */
> Index: mmotm-0827/mm/memcontrol.c
> ===================================================================
> --- mmotm-0827.orig/mm/memcontrol.c
> +++ mmotm-0827/mm/memcontrol.c
> @@ -4141,6 +4141,11 @@ mem_cgroup_create(struct cgroup_subsys *
> if (alloc_mem_cgroup_per_zone_info(mem, node))
> goto free_out;
>
> + error = alloc_css_id(ss, cont, &mem->css);
> + if (error)
> + goto free_out;
> + /* Here, css_id(&mem->css) works. but css_lookup(id)->mem doesn't */
> +
> /* root ? */
> if (cont->parent == NULL) {
> int cpu;
> Index: mmotm-0827/block/blk-cgroup.c
> ===================================================================
> --- mmotm-0827.orig/block/blk-cgroup.c
> +++ mmotm-0827/block/blk-cgroup.c
> @@ -958,9 +958,13 @@ blkiocg_create(struct cgroup_subsys *sub
> {
> struct blkio_cgroup *blkcg;
> struct cgroup *parent = cgroup->parent;
> + int ret;
>
> if (!parent) {
> blkcg = &blkio_root_cgroup;
> + ret = alloc_css_id(subsys, cgroup, &blkcg->css);
> + if (ret)
> + return ERR_PTR(ret);
> goto done;
> }
>
> @@ -971,6 +975,11 @@ blkiocg_create(struct cgroup_subsys *sub
> blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
> if (!blkcg)
> return ERR_PTR(-ENOMEM);
> + ret = alloc_css_id(subsys, cgroup, &blkcg->css);
> + if (ret) {
> + kfree(blkcg);
> + return ERR_PTR(ret);
> + }
>
> blkcg->weight = BLKIO_WEIGHT_DEFAULT;
> done:
> Index: mmotm-0827/Documentation/cgroups/cgroups.txt
> ===================================================================
> --- mmotm-0827.orig/Documentation/cgroups/cgroups.txt
> +++ mmotm-0827/Documentation/cgroups/cgroups.txt
> @@ -621,6 +621,54 @@ and root cgroup. Currently this will onl
> the default hierarchy (which never has sub-cgroups) and a hierarchy
> that is being created/destroyed (and hence has no sub-cgroups).
>
> +3.4 cgroup subsys state IDs.
> +------------
> +When subsystem sets use_id == true, an ID per [cgroup, subsys] is added
> +and it will be tied to cgroup_subsys_state object.
> +
> +When use_id==true can use following interfaces. But please note that
> +allocation/free an ID is subsystem's job because cgroup_subsys_state
> +object's lifetime is subsystem's matter.
> +
> +unsigned short css_id(struct cgroup_subsys_state *css)
> +
> +Returns ID of cgroup_subsys_state
Please add trailing '.' (period character).
> +
> +unsigend short css_depth(struct cgroup_subsys_state *css)
Typo: s/unsigend/unsigned/
> +
> +Returns the level which "css" is exisiting under hierarchy tree.
> +The root cgroup's depth 0, its children are 1, children's children are
> +2....
> +
> +int alloc_css_id(struct struct cgroup_subsys *ss, struct cgroup *newgr,
> + struct cgroup_subsys_state *css);
> +
> +Attach an new ID to given css under subsystem ([ss, cgroup])
> +should be called in ->create() callback.
> +
> +void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css);
> +
> +Free ID attached to "css" under subsystem. Should be called before
> +"css" is freed.
> +
> +struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id);
> +
> +Look up cgroup_subsys_state via ID. Should be called under rcu_read_lock().
> +
> +struct cgroup_subsys_state *css_get_next(struct cgroup_subsys *ss, int id,
> + struct cgroup_subsys_state *root, int *foundid);
> +
> +Returns ID which is under "root" i.e. under sub-directory of "root"
> +cgroup's directory at considering cgroup hierarchy. The order of IDs
> +returned by this function is not sorted. Please be careful.
> +
> +bool css_is_ancestor(struct cgroup_subsys_state *cg,
> + const struct cgroup_subsys_state *root);
To match code: s/cg/child/
> +
> +Returns true if "root" and "cs" is under the same hierarchy and
> +"root" can be found when you see all ->parent from "cs" until
This may be more clear: s/see all/walk all/
> +the root cgroup.
As above: s/cs/child/
> +
> 4. Questions
> ============
>
>
>
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