[RFC 1/3] memcg: restructure mem_cgroup_can_attach()

Michal Hocko
2015-05-26T14:13:48Z

From: Tejun Heo <tj@kernel.org>

Restructure it to lower nesting level and help the planned threadgroup
leader iteration changes.

This is pure reorganization.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
---
mm/memcontrol.c | 61 ++++++++++++++++++++++++++++++---------------------------
1 file changed, 32 insertions(+), 29 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5fd273d22714..f3d92cf0caf4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5001,10 +5001,12 @@ static void mem_cgroup_clear_mc(void)
static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
struct cgroup_taskset *tset)
{
- struct task_struct *p = cgroup_taskset_first(tset);
- int ret = 0;
struct mem_cgroup *memcg = mem_cgroup_from_css(css);
+ struct mem_cgroup *from;
+ struct task_struct *p;
+ struct mm_struct *mm;
unsigned long move_flags;
+ int ret = 0;

/*
* We are now commited to this value whatever it is. Changes in this
@@ -5012,36 +5014,37 @@ static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
* So we need to save it, and keep it going.
*/
move_flags = READ_ONCE(memcg->move_charge_at_immigrate);
- if (move_flags) {
- struct mm_struct *mm;
- struct mem_cgroup *from = mem_cgroup_from_task(p);
+ if (!move_flags)
+ return 0;

- VM_BUG_ON(from == memcg);
+ p = cgroup_taskset_first(tset);
+ from = mem_cgroup_from_task(p);

- mm = get_task_mm(p);
- if (!mm)
- return 0;
- /* We move charges only when we move a owner of the mm */
- if (mm->owner == p) {
- VM_BUG_ON(mc.from);
- VM_BUG_ON(mc.to);
- VM_BUG_ON(mc.precharge);
- VM_BUG_ON(mc.moved_charge);
- VM_BUG_ON(mc.moved_swap);
-
- spin_lock(&mc.lock);
- mc.from = from;
- mc.to = memcg;
- mc.flags = move_flags;
- spin_unlock(&mc.lock);
- /* We set mc.moving_task later */
-
- ret = mem_cgroup_precharge_mc(mm);
- if (ret)
- mem_cgroup_clear_mc();
- }
- mmput(mm);
+ VM_BUG_ON(from == memcg);
+
+ mm = get_task_mm(p);
+ if (!mm)
+ return 0;
+ /* We move charges only when we move a owner of the mm */
+ if (mm->owner == p) {
+ VM_BUG_ON(mc.from);
+ VM_BUG_ON(mc.to);
+ VM_BUG_ON(mc.precharge);
+ VM_BUG_ON(mc.moved_charge);
+ VM_BUG_ON(mc.moved_swap);
+
+ spin_lock(&mc.lock);
+ mc.from = from;
+ mc.to = memcg;
+ mc.flags = move_flags;
+ spin_unlock(&mc.lock);
+ /* We set mc.moving_task later */
+
+ ret = mem_cgroup_precharge_mc(mm);
+ if (ret)
+ mem_cgroup_clear_mc();
}
+ mmput(mm);
return ret;
}

--
2.1.4