memcg: restructure mem_cgroup_can_attach()

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>
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6935f77589e7054284949ad01c0ee237ecd67306..191d8aa5da713e68b1d0167fc1c4b5583838f997 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4834,10 +4834,12 @@ 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
@@ -4845,36 +4847,37 @@ 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;
 }