(2012/11/17 4:20), Tejun Heo wrote:
> With the introduction of generic cgroup hierarchy iterators, css_id is
> being phased out. It was unnecessarily complex, id'ing the wrong
> thing (cgroups need IDs, not CSSes) and has other oddities like not
> being available at ->css_alloc().
>
> This patch adds cgroup->id, which is a simple per-hierarchy
> ida-allocated ID which is assigned before ->css_alloc() and released
> after ->css_free().
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
I'm sorry if I misunderstand ... current usage of css-id in memory/swap cgroup
is for recording information of memory cgroup which may be destroyed. In some case,
a memcg's cgroup is freed but a struct memcgroup and its css are available, swap_cgroup
may contain id ot if.
This patch puts cgroup's id at diput(), so, the id used in swap_cgroup can be
reused while it's in use. Right ?
Thanks,
-Kame
> ---
> include/linux/cgroup.h | 2 ++
> kernel/cgroup.c | 15 ++++++++++++++-
> 2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index d5fc8a7..b512469 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -159,6 +159,8 @@ struct cgroup {
> */
> atomic_t count;
>
> + int id; /* ida allocated in-hierarchy ID */
> +
> /*
> * We link our 'sibling' struct into our parent's 'children'.
> * Our children link their 'sibling' into our 'children'.
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 99d5e69..0b25dcb 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -138,6 +138,9 @@ struct cgroupfs_root {
> /* Hierarchy-specific flags */
> unsigned long flags;
>
> + /* IDs for cgroups in this hierarchy */
> + struct ida cgroup_ida;
> +
> /* The path to use for release notifications. */
> char release_agent_path[PATH_MAX];
>
> @@ -890,6 +893,7 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
>
> simple_xattrs_free(&cgrp->xattrs);
>
> + ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
> kfree(cgrp);
> } else {
> struct cfent *cfe = __d_cfe(dentry);
> @@ -1465,6 +1469,7 @@ static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
>
> root->subsys_mask = opts->subsys_mask;
> root->flags = opts->flags;
> + ida_init(&root->cgroup_ida);
> if (opts->release_agent)
> strcpy(root->release_agent_path, opts->release_agent);
> if (opts->name)
> @@ -1483,6 +1488,7 @@ static void cgroup_drop_root(struct cgroupfs_root *root)
> spin_lock(&hierarchy_id_lock);
> ida_remove(&hierarchy_ida, root->hierarchy_id);
> spin_unlock(&hierarchy_id_lock);
> + ida_destroy(&root->cgroup_ida);
> kfree(root);
> }
>
> @@ -4093,10 +4099,15 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
> struct cgroup_subsys *ss;
> struct super_block *sb = root->sb;
>
> + /* allocate the cgroup and its ID, 0 is reserved for the root */
> cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
> if (!cgrp)
> return -ENOMEM;
>
> + cgrp->id = ida_simple_get(&root->cgroup_ida, 1, 0, GFP_KERNEL);
> + if (cgrp->id < 0)
> + goto err_free_cgrp;
> +
> /*
> * Only live parents can have children. Note that the liveliness
> * check isn't strictly necessary because cgroup_mkdir() and
> @@ -4106,7 +4117,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
> */
> if (!cgroup_lock_live_group(parent)) {
> err = -ENODEV;
> - goto err_free_cgrp;
> + goto err_free_id;
> }
>
> /* Grab a reference on the superblock so the hierarchy doesn't
> @@ -4198,6 +4209,8 @@ err_free_all:
> mutex_unlock(&cgroup_mutex);
> /* Release the reference count that we took on the superblock */
> deactivate_super(sb);
> +err_free_id:
> + ida_simple_remove(&root->cgroup_ida, cgrp->id);
> err_free_cgrp:
> kfree(cgrp);
> return err;
>
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