diff options
| -rw-r--r-- | include/linux/cgroup.h | 15 | ||||
| -rw-r--r-- | kernel/cgroup.c | 65 |
2 files changed, 76 insertions, 4 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index ada239253ec7..4b38e2d6110d 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -154,6 +154,14 @@ struct cgroup { /* the number of attached css's */ int nr_css; + /* + * If this cgroup contains any tasks, it contributes one to + * populated_cnt. All children with non-zero popuplated_cnt of + * their own contribute one. The count is zero iff there's no task + * in this cgroup or its subtree. + */ + int populated_cnt; + atomic_t refcnt; /* @@ -166,6 +174,7 @@ struct cgroup { struct cgroup *parent; /* my parent */ struct kernfs_node *kn; /* cgroup kernfs entry */ struct kernfs_node *control_kn; /* kn for "cgroup.subtree_control" */ + struct kernfs_node *populated_kn; /* kn for "cgroup.subtree_populated" */ /* * Monotonically increasing unique serial number which defines a @@ -264,6 +273,12 @@ enum { * * - "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. * diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 809dd903ceb8..0f986f7afee4 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -411,6 +411,43 @@ static struct css_set init_css_set = { static int css_set_count = 1; /* 1 for init_css_set */ +/** + * cgroup_update_populated - updated populated count of a cgroup + * @cgrp: the target cgroup + * @populated: inc or dec populated count + * + * @cgrp is either getting the first task (css_set) or losing the last. + * Update @cgrp->populated_cnt accordingly. The count is propagated + * towards root so that a given cgroup's populated_cnt is zero iff the + * cgroup and all its descendants are empty. + * + * @cgrp's interface file "cgroup.populated" is zero if + * @cgrp->populated_cnt is zero and 1 otherwise. When @cgrp->populated_cnt + * changes from or to zero, userland is notified that the content of the + * interface file has changed. This can be used to detect when @cgrp and + * its descendants become populated or empty. + */ +static void cgroup_update_populated(struct cgroup *cgrp, bool populated) +{ + lockdep_assert_held(&css_set_rwsem); + + do { + bool trigger; + + if (populated) + trigger = !cgrp->populated_cnt++; + else + trigger = !--cgrp->populated_cnt; + + if (!trigger) + break; + + if (cgrp->populated_kn) + kernfs_notify(cgrp->populated_kn); + cgrp = cgrp->parent; + } while (cgrp); +} + /* * hash table for cgroup groups. This improves the performance to find * an existing css_set. This hash doesn't (currently) take into @@ -456,10 +493,13 @@ static void put_css_set_locked(struct css_set *cset, bool taskexit) list_del(&link->cgrp_link); /* @cgrp can't go away while we're holding css_set_rwsem */ - if (list_empty(&cgrp->cset_links) && notify_on_release(cgrp)) { - if (taskexit) - set_bit(CGRP_RELEASABLE, &cgrp->flags); - check_for_release(cgrp); + if (list_empty(&cgrp->cset_links)) { + cgroup_update_populated(cgrp, false); + if (notify_on_release(cgrp)) { + if (taskexit) + set_bit(CGRP_RELEASABLE, &cgrp->flags); + check_for_release(cgrp); + } } kfree(link); @@ -668,7 +708,11 @@ static void link_css_set(struct list_head *tmp_links, struct css_set *cset, link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link); link->cset = cset; link->cgrp = cgrp; + + if (list_empty(&cgrp->cset_links)) + cgroup_update_populated(cgrp, true); list_move(&link->cset_link, &cgrp->cset_links); + /* * Always add links to the tail of the list so that the list * is sorted by order of hierarchy creation @@ -2643,6 +2687,12 @@ err_undo_css: goto out_unlock; } +static int cgroup_populated_show(struct seq_file *seq, void *v) +{ + seq_printf(seq, "%d\n", (bool)seq_css(seq)->cgroup->populated_cnt); + return 0; +} + static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { @@ -2809,6 +2859,8 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft) if (cft->seq_show == cgroup_subtree_control_show) cgrp->control_kn = kn; + else if (cft->seq_show == cgroup_populated_show) + cgrp->populated_kn = kn; return 0; } @@ -3918,6 +3970,11 @@ static struct cftype cgroup_base_files[] = { .seq_show = cgroup_subtree_control_show, .write_string = cgroup_subtree_control_write, }, + { + .name = "cgroup.populated", + .flags = CFTYPE_ONLY_ON_DFL | CFTYPE_NOT_ON_ROOT, + .seq_show = cgroup_populated_show, + }, /* * Historical crazy stuff. These don't have "cgroup." prefix and |