css_update_populated(9)

💅 css_update_populated(9) 💅

okay bestie, this one's straight from the Kernel API Manual, and it's all about keeping the populated-state vibes accurate all the way up the cgroup family tree. no cap. 🌳✨

🌸 NAME 🌸

css_update_populated — update the populated state of a css and ancestors.

✨ SYNOPSIS ✨

void css_update_populated (struct cgroup_subsys_state *css , bool populated );

🎀 ARGUMENTS 🎀

• css — leaf css whose own populated count is changing. literally the leaf in question, bestie.
• populated — inc or dec. that's the whole mood.

🦋 DESCRIPTION 🦋

okay so picture this: one of the css_sets pinned by css is getting its first task, or it's losing the last one. that's the transition. css_update_populated() propagates that transition up the parent chain so that a css's nr_populated_children is zero iff none of its descendants contain any tasks. the math is mathing. 🧮💖

For a cgroup->self walk, it also runs cgroup-side bookkeeping at each level:

• the domain/threaded child split,
• the deferred-destroy trigger,
• and notification via "cgroup.populated" — zero iff cgrp->self has neither populated csets nor populated children; userland is notified on transitions.

so yeah, it's giving "keep every ancestor's populated tea accurate" and honestly? iconic. 👑

👑 SEE ALSO 👑

Kernel file ./kernel/cgroup/cgroup.c — plus the whole extended function fam, in order, no skips:

• cgroup_ssid_enabled(9), cgroup_on_dfl(9), cgroup_e_css_by_mask(9), cgroup_e_css(9), cgroup_get_e_css(9), __cgroup_task_count(9), cgroup_task_count(9), for_each_css(9), do_each_subsys_mask(9), css_set_populated(9)
• css_set_update_populated(9), css_set_move_task(9), compare_css_sets(9), find_existing_css_set(9), allocate_cgrp_cset_links(9), link_css_set(9), find_css_set(9), cgroup_file_mode(9), cgroup_calc_subtree_ss_mask(9), cgroup_kn_unlock(9)
• cgroup_kn_lock_live(9), css_clear_dir(9), css_populate_dir(9), cgroup_attach_lock(9), cgroup_attach_unlock(9), cgroup_migrate_add_task(9), cgroup_taskset_first(9), cgroup_taskset_next(9), cgroup_migrate_execute(9), cgroup_migrate_vet_dst(9)
• cgroup_migrate_finish(9), cgroup_migrate_add_src(9), cgroup_migrate_prepare_dst(9), cgroup_migrate(9), cgroup_attach_task(9), cgroup_update_dfl_csses(9), cgroup_lock_and_drain_offline(9), cgroup_save_control(9), cgroup_propagate_control(9), cgroup_restore_control(9)
• cgroup_apply_control_enable(9), cgroup_apply_control_disable(9), cgroup_apply_control(9), cgroup_finalize_control(9), cgroup_enable_threaded(9), cgroup_tryget_css(9), cgroup_addrm_files(9), cgroup_rm_cftypes(9), cgroup_add_cftypes(9), cgroup_add_dfl_cftypes(9)
• cgroup_add_legacy_cftypes(9), cgroup_file_notify(9), cgroup_file_show(9), css_next_child(9), css_next_descendant_pre(9), css_rightmost_descendant(9), css_next_descendant_post(9), css_has_online_children(9), css_task_iter_advance_css_set(9), css_task_iter_start(9)
• css_task_iter_next(9), css_task_iter_end(9), css_create(9), kill_css_sync(9), kill_css_finish(9), cgroup_destroy_locked(9), cgroup_init_early(9), cgroup_init(9), cgroup_fork(9), cgroup_v1v2_get_from_file(9)
• cgroup_get_from_file(9), cgroup_css_set_fork(9), cgroup_css_set_put_fork(9), cgroup_can_fork(9), cgroup_cancel_fork(9), cgroup_post_fork(9), cgroup_task_exit(9), css_tryget_online_from_dir(9), css_from_id(9), cgroup_get_from_path(9)
• cgroup_v1v2_get_from_fd(9), cgroup_get_from_fd(9), cgroup_parse_float(9)

xoxo bestie 💖 that was css_update_populated(9) from ./kernel/cgroup, stamped October 2026. slay responsibly. 🎀✨