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cgroup: reorganize css_task_iter

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This patch reorganizes css_task_iter so that adding effective css
support is easier.

* s/->cset_link/->cset_pos/ and s/->task/->task_pos/ for consistency

* ->origin_css is used to determine whether the iteration reached the
  last css_set.  Replace it with explicit ->cset_head so that
  css_advance_task_iter() doesn't have to know the termination
  condition directly.

* css_task_iter_next() currently assumes that it's walking list of
  cgrp_cset_link and reaches into the current cset through the current
  link to determine the termination conditions for task walking.  As
  this won't always be true for effective css walking, add
  ->tasks_head and ->mg_tasks_head and use them to control task
  walking so that css_task_iter_next() doesn't have to know how
  css_sets are being walked.

This patch doesn't make any behavior changes.  The iteration logic
stays unchanged after the patch.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2014-04-23 11:13:15 -04:00
parent 3b281afbc3
commit 0f0a2b4fa6
2 changed files with 23 additions and 19 deletions
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9
include/linux/cgroup.h
View File

@ -842,9 +842,12 @@ css_next_descendant_post(struct cgroup_subsys_state *pos,
/* A css_task_iter should be treated as an opaque object */
struct css_task_iter {
struct cgroup_subsys_state *origin_css;
struct list_head *cset_link;
struct list_head *task;
struct list_head *cset_pos;
struct list_head *cset_head;
struct list_head *task_pos;
struct list_head *tasks_head;
struct list_head *mg_tasks_head;
};
void css_task_iter_start(struct cgroup_subsys_state *css,

33
kernel/cgroup.c
View File

@ -2857,27 +2857,30 @@ css_next_descendant_post(struct cgroup_subsys_state *pos,
*/
static void css_advance_task_iter(struct css_task_iter *it)
{
struct list_head *l = it->cset_link;
struct list_head *l = it->cset_pos;
struct cgrp_cset_link *link;
struct css_set *cset;
/* Advance to the next non-empty css_set */
do {
l = l->next;
if (l == &it->origin_css->cgroup->cset_links) {
it->cset_link = NULL;
if (l == it->cset_head) {
it->cset_pos = NULL;
return;
}
link = list_entry(l, struct cgrp_cset_link, cset_link);
cset = link->cset;
} while (list_empty(&cset->tasks) && list_empty(&cset->mg_tasks));
it->cset_link = l;
it->cset_pos = l;
if (!list_empty(&cset->tasks))
it->task = cset->tasks.next;
it->task_pos = cset->tasks.next;
else
it->task = cset->mg_tasks.next;
it->task_pos = cset->mg_tasks.next;
it->tasks_head = &cset->tasks;
it->mg_tasks_head = &cset->mg_tasks;
}
/**
@ -2903,8 +2906,8 @@ void css_task_iter_start(struct cgroup_subsys_state *css,
down_read(&css_set_rwsem);
it->origin_css = css;
it->cset_link = &css->cgroup->cset_links;
it->cset_pos = &css->cgroup->cset_links;
it->cset_head = it->cset_pos;
css_advance_task_iter(it);
}
@ -2920,12 +2923,10 @@ void css_task_iter_start(struct cgroup_subsys_state *css,
struct task_struct *css_task_iter_next(struct css_task_iter *it)
{
struct task_struct *res;
struct list_head *l = it->task;
struct cgrp_cset_link *link = list_entry(it->cset_link,
struct cgrp_cset_link, cset_link);
struct list_head *l = it->task_pos;
/* If the iterator cg is NULL, we have no tasks */
if (!it->cset_link)
if (!it->cset_pos)
return NULL;
res = list_entry(l, struct task_struct, cg_list);
@ -2936,13 +2937,13 @@ struct task_struct *css_task_iter_next(struct css_task_iter *it)
*/
l = l->next;
if (l == &link->cset->tasks)
l = link->cset->mg_tasks.next;
if (l == it->tasks_head)
l = it->mg_tasks_head->next;
if (l == &link->cset->mg_tasks)
if (l == it->mg_tasks_head)
css_advance_task_iter(it);
else
it->task = l;
it->task_pos = l;
return res;
}