memcg: use for_each_mem_cgroup
In memory cgroup management, we sometimes have to walk through
subhierarchy of cgroup to gather informaiton, or lock something, etc.
Now, to do that, mem_cgroup_walk_tree() function is provided. It calls
given callback function per cgroup found. But the bad thing is that it
has to pass a fixed style function and argument, "void*" and it adds much
type casting to memcontrol.c.
To make the code clean, this patch replaces walk_tree() with
for_each_mem_cgroup_tree(iter, root)
An iterator style call. The good point is that iterator call doesn't have
to assume what kind of function is called under it. A bad point is that
it may cause reference-count leak if a caller use "break" from the loop by
mistake.
I think the benefit is larger. The modified code seems straigtforward and
easy to read because we don't have misterious callbacks and pointer cast.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
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 dd845d2..5e7a14d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -660,41 +660,58 @@
return mem;
}
-/*
- * Call callback function against all cgroup under hierarchy tree.
- */
-static int mem_cgroup_walk_tree(struct mem_cgroup *root, void *data,
- int (*func)(struct mem_cgroup *, void *))
+/* The caller has to guarantee "mem" exists before calling this */
+static struct mem_cgroup *mem_cgroup_start_loop(struct mem_cgroup *mem)
{
- int found, ret, nextid;
- struct cgroup_subsys_state *css;
- struct mem_cgroup *mem;
-
- if (!root->use_hierarchy)
- return (*func)(root, data);
-
- nextid = 1;
- do {
- ret = 0;
- mem = NULL;
-
- rcu_read_lock();
- css = css_get_next(&mem_cgroup_subsys, nextid, &root->css,
- &found);
- if (css && css_tryget(css))
- mem = container_of(css, struct mem_cgroup, css);
- rcu_read_unlock();
-
- if (mem) {
- ret = (*func)(mem, data);
- css_put(&mem->css);
- }
- nextid = found + 1;
- } while (!ret && css);
-
- return ret;
+ if (mem && css_tryget(&mem->css))
+ return mem;
+ return NULL;
}
+static struct mem_cgroup *mem_cgroup_get_next(struct mem_cgroup *iter,
+ struct mem_cgroup *root,
+ bool cond)
+{
+ int nextid = css_id(&iter->css) + 1;
+ int found;
+ int hierarchy_used;
+ struct cgroup_subsys_state *css;
+
+ hierarchy_used = iter->use_hierarchy;
+
+ css_put(&iter->css);
+ if (!cond || !hierarchy_used)
+ return NULL;
+
+ do {
+ iter = NULL;
+ rcu_read_lock();
+
+ css = css_get_next(&mem_cgroup_subsys, nextid,
+ &root->css, &found);
+ if (css && css_tryget(css))
+ iter = container_of(css, struct mem_cgroup, css);
+ rcu_read_unlock();
+ /* If css is NULL, no more cgroups will be found */
+ nextid = found + 1;
+ } while (css && !iter);
+
+ return iter;
+}
+/*
+ * for_eacn_mem_cgroup_tree() for visiting all cgroup under tree. Please
+ * be careful that "break" loop is not allowed. We have reference count.
+ * Instead of that modify "cond" to be false and "continue" to exit the loop.
+ */
+#define for_each_mem_cgroup_tree_cond(iter, root, cond) \
+ for (iter = mem_cgroup_start_loop(root);\
+ iter != NULL;\
+ iter = mem_cgroup_get_next(iter, root, cond))
+
+#define for_each_mem_cgroup_tree(iter, root) \
+ for_each_mem_cgroup_tree_cond(iter, root, true)
+
+
static inline bool mem_cgroup_is_root(struct mem_cgroup *mem)
{
return (mem == root_mem_cgroup);
@@ -1132,13 +1149,6 @@
return false;
}
-static int mem_cgroup_count_children_cb(struct mem_cgroup *mem, void *data)
-{
- int *val = data;
- (*val)++;
- return 0;
-}
-
/**
* mem_cgroup_print_oom_info: Called from OOM with tasklist_lock held in read mode.
* @memcg: The memory cgroup that went over limit
@@ -1213,7 +1223,10 @@
static int mem_cgroup_count_children(struct mem_cgroup *mem)
{
int num = 0;
- mem_cgroup_walk_tree(mem, &num, mem_cgroup_count_children_cb);
+ struct mem_cgroup *iter;
+
+ for_each_mem_cgroup_tree(iter, mem)
+ num++;
return num;
}
@@ -1362,49 +1375,39 @@
return total;
}
-static int mem_cgroup_oom_lock_cb(struct mem_cgroup *mem, void *data)
-{
- int *val = (int *)data;
- int x;
- /*
- * Logically, we can stop scanning immediately when we find
- * a memcg is already locked. But condidering unlock ops and
- * creation/removal of memcg, scan-all is simple operation.
- */
- x = atomic_inc_return(&mem->oom_lock);
- *val = max(x, *val);
- return 0;
-}
/*
* Check OOM-Killer is already running under our hierarchy.
* If someone is running, return false.
*/
static bool mem_cgroup_oom_lock(struct mem_cgroup *mem)
{
- int lock_count = 0;
+ int x, lock_count = 0;
+ struct mem_cgroup *iter;
- mem_cgroup_walk_tree(mem, &lock_count, mem_cgroup_oom_lock_cb);
+ for_each_mem_cgroup_tree(iter, mem) {
+ x = atomic_inc_return(&iter->oom_lock);
+ lock_count = max(x, lock_count);
+ }
if (lock_count == 1)
return true;
return false;
}
-static int mem_cgroup_oom_unlock_cb(struct mem_cgroup *mem, void *data)
+static int mem_cgroup_oom_unlock(struct mem_cgroup *mem)
{
+ struct mem_cgroup *iter;
+
/*
* When a new child is created while the hierarchy is under oom,
* mem_cgroup_oom_lock() may not be called. We have to use
* atomic_add_unless() here.
*/
- atomic_add_unless(&mem->oom_lock, -1, 0);
+ for_each_mem_cgroup_tree(iter, mem)
+ atomic_add_unless(&iter->oom_lock, -1, 0);
return 0;
}
-static void mem_cgroup_oom_unlock(struct mem_cgroup *mem)
-{
- mem_cgroup_walk_tree(mem, NULL, mem_cgroup_oom_unlock_cb);
-}
static DEFINE_MUTEX(memcg_oom_mutex);
static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);
@@ -3207,33 +3210,25 @@
return retval;
}
-struct mem_cgroup_idx_data {
- s64 val;
- enum mem_cgroup_stat_index idx;
-};
-static int
-mem_cgroup_get_idx_stat(struct mem_cgroup *mem, void *data)
+static u64 mem_cgroup_get_recursive_idx_stat(struct mem_cgroup *mem,
+ enum mem_cgroup_stat_index idx)
{
- struct mem_cgroup_idx_data *d = data;
- d->val += mem_cgroup_read_stat(mem, d->idx);
- return 0;
-}
+ struct mem_cgroup *iter;
+ s64 val = 0;
-static void
-mem_cgroup_get_recursive_idx_stat(struct mem_cgroup *mem,
- enum mem_cgroup_stat_index idx, s64 *val)
-{
- struct mem_cgroup_idx_data d;
- d.idx = idx;
- d.val = 0;
- mem_cgroup_walk_tree(mem, &d, mem_cgroup_get_idx_stat);
- *val = d.val;
+ /* each per cpu's value can be minus.Then, use s64 */
+ for_each_mem_cgroup_tree(iter, mem)
+ val += mem_cgroup_read_stat(iter, idx);
+
+ if (val < 0) /* race ? */
+ val = 0;
+ return val;
}
static inline u64 mem_cgroup_usage(struct mem_cgroup *mem, bool swap)
{
- u64 idx_val, val;
+ u64 val;
if (!mem_cgroup_is_root(mem)) {
if (!swap)
@@ -3242,16 +3237,12 @@
return res_counter_read_u64(&mem->memsw, RES_USAGE);
}
- mem_cgroup_get_recursive_idx_stat(mem, MEM_CGROUP_STAT_CACHE, &idx_val);
- val = idx_val;
- mem_cgroup_get_recursive_idx_stat(mem, MEM_CGROUP_STAT_RSS, &idx_val);
- val += idx_val;
+ val = mem_cgroup_get_recursive_idx_stat(mem, MEM_CGROUP_STAT_CACHE);
+ val += mem_cgroup_get_recursive_idx_stat(mem, MEM_CGROUP_STAT_RSS);
- if (swap) {
- mem_cgroup_get_recursive_idx_stat(mem,
- MEM_CGROUP_STAT_SWAPOUT, &idx_val);
- val += idx_val;
- }
+ if (swap)
+ val += mem_cgroup_get_recursive_idx_stat(mem,
+ MEM_CGROUP_STAT_SWAPOUT);
return val << PAGE_SHIFT;
}
@@ -3459,9 +3450,9 @@
};
-static int mem_cgroup_get_local_stat(struct mem_cgroup *mem, void *data)
+static void
+mem_cgroup_get_local_stat(struct mem_cgroup *mem, struct mcs_total_stat *s)
{
- struct mcs_total_stat *s = data;
s64 val;
/* per cpu stat */
@@ -3491,13 +3482,15 @@
s->stat[MCS_ACTIVE_FILE] += val * PAGE_SIZE;
val = mem_cgroup_get_local_zonestat(mem, LRU_UNEVICTABLE);
s->stat[MCS_UNEVICTABLE] += val * PAGE_SIZE;
- return 0;
}
static void
mem_cgroup_get_total_stat(struct mem_cgroup *mem, struct mcs_total_stat *s)
{
- mem_cgroup_walk_tree(mem, s, mem_cgroup_get_local_stat);
+ struct mem_cgroup *iter;
+
+ for_each_mem_cgroup_tree(iter, mem)
+ mem_cgroup_get_local_stat(iter, s);
}
static int mem_control_stat_show(struct cgroup *cont, struct cftype *cft,
@@ -3674,7 +3667,7 @@
return _a->threshold - _b->threshold;
}
-static int mem_cgroup_oom_notify_cb(struct mem_cgroup *mem, void *data)
+static int mem_cgroup_oom_notify_cb(struct mem_cgroup *mem)
{
struct mem_cgroup_eventfd_list *ev;
@@ -3685,7 +3678,10 @@
static void mem_cgroup_oom_notify(struct mem_cgroup *mem)
{
- mem_cgroup_walk_tree(mem, NULL, mem_cgroup_oom_notify_cb);
+ struct mem_cgroup *iter;
+
+ for_each_mem_cgroup_tree(iter, mem)
+ mem_cgroup_oom_notify_cb(iter);
}
static int mem_cgroup_usage_register_event(struct cgroup *cgrp,
