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Message-Id: <1444447781-16182-3-git-send-email-tj@kernel.org> Date: Fri, 9 Oct 2015 23:29:29 -0400 From: Tejun Heo <tj@...nel.org> To: lizefan@...wei.com, hannes@...xchg.org Cc: cgroups@...r.kernel.org, cyphar@...har.com, linux-kernel@...r.kernel.org, kernel-team@...com, Tejun Heo <tj@...nel.org> Subject: [PATCH 02/14] cgroup: make cgroup->nr_populated count the number of populated css_sets Currently, cgroup->nr_populated counts whether the cgroup has any css_sets linked to it and the number of children which has non-zero ->nr_populated. This works because a css_set's refcnt converges with the number of tasks linked to it and thus there's no css_set linked to a cgroup if it doesn't have any live tasks. To help tracking resource usage of zombie tasks, putting the ref of css_set will be separated from disassociating the task from the css_set which means that a cgroup may have css_sets linked to it even when it doesn't have any live tasks. This patch updates cgroup->nr_populated so that for the cgroup itself it counts the number of css_sets which have tasks associated with them so that empty css_sets don't skew the populated test. Signed-off-by: Tejun Heo <tj@...nel.org> --- include/linux/cgroup-defs.h | 8 +++--- kernel/cgroup.c | 65 ++++++++++++++++++++++++++++++++++++--------- 2 files changed, 56 insertions(+), 17 deletions(-) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index df589a0..1744450 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -232,10 +232,10 @@ struct cgroup { int id; /* - * 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. + * Each non-empty css_set associated with this cgroup 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; diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 49f30f1..e5231d0 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -582,14 +582,25 @@ struct css_set init_css_set = { static int css_set_count = 1; /* 1 for init_css_set */ /** + * css_set_populated - does a css_set contain any tasks? + * @cset: target css_set + */ +static bool css_set_populated(struct css_set *cset) +{ + lockdep_assert_held(&css_set_rwsem); + + return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks); +} + +/** * 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. + * One of the css_sets associated with @cgrp is either getting its first + * task 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 don't contain any tasks. * * @cgrp's interface file "cgroup.populated" is zero if * @cgrp->populated_cnt is zero and 1 otherwise. When @cgrp->populated_cnt @@ -618,6 +629,24 @@ static void cgroup_update_populated(struct cgroup *cgrp, bool populated) } while (cgrp); } +/** + * css_set_update_populated - update populated state of a css_set + * @cset: target css_set + * @populated: whether @cset is populated or depopulated + * + * @cset is either getting the first task or losing the last. Update the + * ->populated_cnt of all associated cgroups accordingly. + */ +static void css_set_update_populated(struct css_set *cset, bool populated) +{ + struct cgrp_cset_link *link; + + lockdep_assert_held(&css_set_rwsem); + + list_for_each_entry(link, &cset->cgrp_links, cgrp_link) + cgroup_update_populated(link->cgrp, populated); +} + /* * hash table for cgroup groups. This improves the performance to find * an existing css_set. This hash doesn't (currently) take into @@ -663,10 +692,8 @@ static void put_css_set_locked(struct css_set *cset) list_del(&link->cgrp_link); /* @cgrp can't go away while we're holding css_set_rwsem */ - if (list_empty(&cgrp->cset_links)) { - cgroup_update_populated(cgrp, false); + if (list_empty(&cgrp->cset_links)) check_for_release(cgrp); - } kfree(link); } @@ -875,8 +902,6 @@ static void link_css_set(struct list_head *tmp_links, struct css_set *cset, 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); /* @@ -1754,6 +1779,8 @@ static void cgroup_enable_task_cg_lists(void) if (!(p->flags & PF_EXITING)) { struct css_set *cset = task_css_set(p); + if (!css_set_populated(cset)) + css_set_update_populated(cset, true); list_add(&p->cg_list, &cset->tasks); get_css_set(cset); } @@ -1868,8 +1895,11 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask) * objects. */ down_write(&css_set_rwsem); - hash_for_each(css_set_table, i, cset, hlist) + hash_for_each(css_set_table, i, cset, hlist) { link_css_set(&tmp_links, cset, root_cgrp); + if (css_set_populated(cset)) + cgroup_update_populated(root_cgrp, true); + } up_write(&css_set_rwsem); BUG_ON(!list_empty(&root_cgrp->self.children)); @@ -2256,10 +2286,16 @@ static void cgroup_task_migrate(struct task_struct *tsk, WARN_ON_ONCE(tsk->flags & PF_EXITING); old_cset = task_css_set(tsk); + if (!css_set_populated(new_cset)) + css_set_update_populated(new_cset, true); + get_css_set(new_cset); rcu_assign_pointer(tsk->cgroups, new_cset); list_move_tail(&tsk->cg_list, &new_cset->mg_tasks); + if (!css_set_populated(old_cset)) + css_set_update_populated(old_cset, false); + /* * We just gained a reference on old_cset by taking it from the * task. As trading it for new_cset is protected by cgroup_mutex, @@ -3774,7 +3810,7 @@ static void css_advance_task_iter(struct css_task_iter *it) link = list_entry(l, struct cgrp_cset_link, cset_link); cset = link->cset; } - } while (list_empty(&cset->tasks) && list_empty(&cset->mg_tasks)); + } while (!css_set_populated(cset)); it->cset_pos = l; @@ -5492,17 +5528,20 @@ void cgroup_exit(struct task_struct *tsk) /* * Unlink from @tsk from its css_set. As migration path can't race - * with us, we can check cg_list without grabbing css_set_rwsem. + * with us, we can check css_set and cg_list without synchronization. */ + cset = task_css_set(tsk); + if (!list_empty(&tsk->cg_list)) { down_write(&css_set_rwsem); list_del_init(&tsk->cg_list); + if (!css_set_populated(cset)) + css_set_update_populated(cset, false); up_write(&css_set_rwsem); put_cset = true; } /* Reassign the task to the init_css_set. */ - cset = task_css_set(tsk); RCU_INIT_POINTER(tsk->cgroups, &init_css_set); /* see cgroup_post_fork() for details */ -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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