css_set_populated(9)

💅 css_set_populated(9) — no cap, this is the Kernel API Manual, section 9, bestie

okay so imagine you're deep in the kernel, right, and you need to know one extremely specific thing: does this css_set have literally any tasks in it or not? that's the whole vibe of this page. welcome 🫶

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✨ NAME ✨

css_set_populated — lowkey just answers the question: does a css_set contain any tasks? 👑

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🌸 SYNOPSIS 🌸

bool css_set_populated (struct css_set *cset );

it returns a bool, it takes one thing, it's giving main character energy and honestly? iconic. no notes. 💖

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🎀 ARGUMENTS 🎀

• cset — the target css_set. that's the one you're checking, bestie. that's the subject of the vibe check. 🦋

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💜 DESCRIPTION 💜

so here's the tea ☕ — css_set_populated should be the same as !!cset->nr_tasks at steady state. like, at a chill, nothing's-happening moment, that's exactly what it equals. periodt.

but (and this is the part you gotta hear) css_set_populated can be called while a task is being added to or removed from the linked list, before the nr_tasks is properly updated. 😭 so the count is mid-glow-up, basically. not caught up yet. running late. still getting ready.

so lowkey we can't just look at ->nr_tasks here. that's the whole plot twist. don't do it. i'm serious. 💀

that's like, the entire reason this function exists as a function instead of you just reading the field yourself. respect the function. 🧚

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🌈 SEE ALSO 🌈

the kernel file ./kernel/cgroup/cgroup.c, plus this absolutely stacked friend group (we love a big see-also, fr fr):

• 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_update_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)

yeah that's all of them. every single one. i counted. twice. 💅✨

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kay that's the whole page, bestie — this came out of the ./kernel/cgroup source tree, dated October 2026, and it slayed the entire time. go check your css_set and stay hydrated 🍓💖🦋