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)
{
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
+ * 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 */
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
+
+unsigend short css_depth(struct cgroup_subsys_state *css)
+
+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);
+
+Returns true if "root" and "cs" is under the same hierarchy and
+"root" can be found when you see all ->parent from "cs" until
+the root cgroup.
+
4. Questions
============
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