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memcg: further simplify mem_cgroup_iter

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mem_cgroup_iter basically does two things currently.  It takes care of
the house keeping (reference counting, raclaim cookie) and it iterates
through a hierarchy tree (by using cgroup generic tree walk).  The code
would be much more easier to follow if we move the iteration outside of
the function (to __mem_cgrou_iter_next) so the distinction is more
clear.  This patch doesn't introduce any functional changes.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Ying Han <yinghan@google.com>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Glauber Costa <glommer@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michal Hocko 2013-04-29 15:07:19 -07:00 committed by Linus Torvalds
parent 19f3940286
commit 16248d8fe6
1 changed files with 46 additions and 33 deletions
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79
mm/memcontrol.c
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@ -1073,6 +1073,51 @@ struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)
return memcg;
}
/*
* Returns a next (in a pre-order walk) alive memcg (with elevated css
* ref. count) or NULL if the whole root's subtree has been visited.
*
* helper function to be used by mem_cgroup_iter
*/
static struct mem_cgroup *__mem_cgroup_iter_next(struct mem_cgroup *root,
struct mem_cgroup *last_visited)
{
struct cgroup *prev_cgroup, *next_cgroup;
/*
* Root is not visited by cgroup iterators so it needs an
* explicit visit.
*/
if (!last_visited)
return root;
prev_cgroup = (last_visited == root) ? NULL
: last_visited->css.cgroup;
skip_node:
next_cgroup = cgroup_next_descendant_pre(
prev_cgroup, root->css.cgroup);
/*
* Even if we found a group we have to make sure it is
* alive. css && !memcg means that the groups should be
* skipped and we should continue the tree walk.
* last_visited css is safe to use because it is
* protected by css_get and the tree walk is rcu safe.
*/
if (next_cgroup) {
struct mem_cgroup *mem = mem_cgroup_from_cont(
next_cgroup);
if (css_tryget(&mem->css))
return mem;
else {
prev_cgroup = next_cgroup;
goto skip_node;
}
}
return NULL;
}
/**
* mem_cgroup_iter - iterate over memory cgroup hierarchy
* @root: hierarchy root
@ -1153,39 +1198,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
}
}
/*
* Root is not visited by cgroup iterators so it needs an
* explicit visit.
*/
if (!last_visited) {
memcg = root;
} else {
struct cgroup *prev_cgroup, *next_cgroup;
prev_cgroup = (last_visited == root) ? NULL
: last_visited->css.cgroup;
skip_node:
next_cgroup = cgroup_next_descendant_pre(
prev_cgroup, root->css.cgroup);
/*
* Even if we found a group we have to make sure it is
* alive. css && !memcg means that the groups should be
* skipped and we should continue the tree walk.
* last_visited css is safe to use because it is
* protected by css_get and the tree walk is rcu safe.
*/
if (next_cgroup) {
struct mem_cgroup *mem = mem_cgroup_from_cont(
next_cgroup);
if (css_tryget(&mem->css))
memcg = mem;
else {
prev_cgroup = next_cgroup;
goto skip_node;
}
}
}
memcg = __mem_cgroup_iter_next(root, last_visited);
if (reclaim) {
if (last_visited)