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Subject[PATCH 05/12] cgroup: reorganize css_task_iter
Date
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>
---
include/linux/cgroup.h | 9 ++++++---
kernel/cgroup.c | 33 +++++++++++++++++----------------
2 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 33a0043..bee3905 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -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,
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f525578..bcf390f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2861,27 +2861,30 @@ 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;
}

/**
@@ -2907,8 +2910,8 @@ 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);
}
@@ -2924,12 +2927,10 @@ 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);

@@ -2940,13 +2941,13 @@ 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;
}
--
1.9.0


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