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Subject[RFC][PATCH 2/4] memcg: use CSS ID in memcg

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Use css ID in memcg.

Assigning CSS ID for each memcg and use css_get_next() for scanning hierarchy.

Assume folloing tree.

group_A (ID=3)
/01 (ID=4)
/0A (ID=7)
/02 (ID=10)
group_B (ID=5)
and task in group_A/01/0A hits limit at group_A.

reclaim will be done in following order (round-robin).
group_A(3) -> group_A/01 (4) -> group_A/01/0A (7) -> group_A/02(10)
-> group_A -> .....

Round robin by ID. The last visited cgroup is recorded and restart
from it when it start reclaim again.
(More smart algorithm can be implemented..)

No cgroup_mutex or hierarchy_mutex is required.

Changelog (v1) -> (v2)
- Updated texts.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

---
mm/memcontrol.c | 219 ++++++++++++++++++++------------------------------------
1 file changed, 81 insertions(+), 138 deletions(-)

Index: mmotm-2.6.28-Jan7/mm/memcontrol.c
===================================================================
--- mmotm-2.6.28-Jan7.orig/mm/memcontrol.c
+++ mmotm-2.6.28-Jan7/mm/memcontrol.c
@@ -154,9 +154,10 @@ struct mem_cgroup {

/*
* While reclaiming in a hiearchy, we cache the last child we
- * reclaimed from. Protected by hierarchy_mutex
+ * reclaimed from.
*/
- struct mem_cgroup *last_scanned_child;
+ int last_scanned_child;
+ unsigned long scan_age;
/*
* Should the accounting and control be hierarchical, per subtree?
*/
@@ -613,103 +614,6 @@ unsigned long mem_cgroup_isolate_pages(u
#define mem_cgroup_from_res_counter(counter, member) \
container_of(counter, struct mem_cgroup, member)

-/*
- * This routine finds the DFS walk successor. This routine should be
- * called with hierarchy_mutex held
- */
-static struct mem_cgroup *
-mem_cgroup_get_next_node(struct mem_cgroup *curr, struct mem_cgroup *root_mem)
-{
- struct cgroup *cgroup, *curr_cgroup, *root_cgroup;
-
- curr_cgroup = curr->css.cgroup;
- root_cgroup = root_mem->css.cgroup;
-
- if (!list_empty(&curr_cgroup->children)) {
- /*
- * Walk down to children
- */
- mem_cgroup_put(curr);
- cgroup = list_entry(curr_cgroup->children.next,
- struct cgroup, sibling);
- curr = mem_cgroup_from_cont(cgroup);
- mem_cgroup_get(curr);
- goto done;
- }
-
-visit_parent:
- if (curr_cgroup == root_cgroup) {
- mem_cgroup_put(curr);
- curr = root_mem;
- mem_cgroup_get(curr);
- goto done;
- }
-
- /*
- * Goto next sibling
- */
- if (curr_cgroup->sibling.next != &curr_cgroup->parent->children) {
- mem_cgroup_put(curr);
- cgroup = list_entry(curr_cgroup->sibling.next, struct cgroup,
- sibling);
- curr = mem_cgroup_from_cont(cgroup);
- mem_cgroup_get(curr);
- goto done;
- }
-
- /*
- * Go up to next parent and next parent's sibling if need be
- */
- curr_cgroup = curr_cgroup->parent;
- goto visit_parent;
-
-done:
- root_mem->last_scanned_child = curr;
- return curr;
-}
-
-/*
- * Visit the first child (need not be the first child as per the ordering
- * of the cgroup list, since we track last_scanned_child) of @mem and use
- * that to reclaim free pages from.
- */
-static struct mem_cgroup *
-mem_cgroup_get_first_node(struct mem_cgroup *root_mem)
-{
- struct cgroup *cgroup;
- struct mem_cgroup *ret;
- bool obsolete;
-
- obsolete = mem_cgroup_is_obsolete(root_mem->last_scanned_child);
-
- /*
- * Scan all children under the mem_cgroup mem
- */
- mutex_lock(&mem_cgroup_subsys.hierarchy_mutex);
- if (list_empty(&root_mem->css.cgroup->children)) {
- ret = root_mem;
- goto done;
- }
-
- if (!root_mem->last_scanned_child || obsolete) {
-
- if (obsolete && root_mem->last_scanned_child)
- mem_cgroup_put(root_mem->last_scanned_child);
-
- cgroup = list_first_entry(&root_mem->css.cgroup->children,
- struct cgroup, sibling);
- ret = mem_cgroup_from_cont(cgroup);
- mem_cgroup_get(ret);
- } else
- ret = mem_cgroup_get_next_node(root_mem->last_scanned_child,
- root_mem);
-
-done:
- root_mem->last_scanned_child = ret;
- mutex_unlock(&mem_cgroup_subsys.hierarchy_mutex);
- return ret;
-}
-
static bool mem_cgroup_check_under_limit(struct mem_cgroup *mem)
{
if (do_swap_account) {
@@ -739,49 +643,84 @@ static unsigned int get_swappiness(struc
}

/*
- * Dance down the hierarchy if needed to reclaim memory. We remember the
- * last child we reclaimed from, so that we don't end up penalizing
- * one child extensively based on its position in the children list.
+ * Visit the first child (need not be the first child as per the ordering
+ * of the cgroup list, since we track last_scanned_child) of @mem and use
+ * that to reclaim free pages from.
+ */
+static struct mem_cgroup *
+mem_cgroup_select_victim(struct mem_cgroup *root_mem)
+{
+ struct mem_cgroup *ret = NULL;
+ struct cgroup_subsys_state *css;
+ int nextid, found;
+
+ if (!root_mem->use_hierarchy) {
+ spin_lock(&root_mem->reclaim_param_lock);
+ root_mem->scan_age++;
+ spin_unlock(&root_mem->reclaim_param_lock);
+ css_get(&root_mem->css);
+ ret = root_mem;
+ }
+
+ while (!ret) {
+ rcu_read_lock();
+ nextid = root_mem->last_scanned_child + 1;
+ css = css_get_next(&mem_cgroup_subsys, nextid, &root_mem->css,
+ &found);
+ if (css && css_tryget(css))
+ ret = container_of(css, struct mem_cgroup, css);
+
+ rcu_read_unlock();
+ /* Updates scanning parameter */
+ spin_lock(&root_mem->reclaim_param_lock);
+ if (!css) {
+ /* this means start scan from ID:1 */
+ root_mem->last_scanned_child = 0;
+ root_mem->scan_age++;
+ } else
+ root_mem->last_scanned_child = found;
+ spin_unlock(&root_mem->reclaim_param_lock);
+ }
+
+ return ret;
+}
+
+/*
+ * Scan the hierarchy if needed to reclaim memory. We remember the last child
+ * we reclaimed from, so that we don't end up penalizing one child extensively
+ * based on its position in the children list.
*
* root_mem is the original ancestor that we've been reclaim from.
+ *
+ * scan_age is updated every time when select_victim returns "root" and
+ * it's shared under system (per hierarchy root).
+ *
+ * We give up and return to the caller when scan_age is increased by 2. This
+ * means try_to_free_mem_cgroup_pages() is called against all children cgroup,
+ * at least once. The caller itself will do further retry if necessary.
*/
static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
gfp_t gfp_mask, bool noswap)
{
- struct mem_cgroup *next_mem;
- int ret = 0;
-
- /*
- * Reclaim unconditionally and don't check for return value.
- * We need to reclaim in the current group and down the tree.
- * One might think about checking for children before reclaiming,
- * but there might be left over accounting, even after children
- * have left.
- */
- ret = try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap,
- get_swappiness(root_mem));
- if (mem_cgroup_check_under_limit(root_mem))
- return 0;
- if (!root_mem->use_hierarchy)
- return ret;
-
- next_mem = mem_cgroup_get_first_node(root_mem);
-
- while (next_mem != root_mem) {
- if (mem_cgroup_is_obsolete(next_mem)) {
- mem_cgroup_put(next_mem);
- next_mem = mem_cgroup_get_first_node(root_mem);
- continue;
- }
- ret = try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap,
- get_swappiness(next_mem));
+ struct mem_cgroup *victim;
+ unsigned long start_age;
+ int ret, total = 0;
+ /*
+ * Reclaim memory from cgroups under root_mem in round robin.
+ */
+ start_age = root_mem->scan_age;
+
+ while (time_after((start_age + 2UL), root_mem->scan_age)) {
+ victim = mem_cgroup_select_victim(root_mem);
+ /* we use swappiness of local cgroup */
+ ret = try_to_free_mem_cgroup_pages(victim, gfp_mask, noswap,
+ get_swappiness(victim));
+ css_put(&victim->css);
+ total += ret;
if (mem_cgroup_check_under_limit(root_mem))
- return 0;
- mutex_lock(&mem_cgroup_subsys.hierarchy_mutex);
- next_mem = mem_cgroup_get_next_node(next_mem, root_mem);
- mutex_unlock(&mem_cgroup_subsys.hierarchy_mutex);
+ return 1 + total;
}
- return ret;
+ return total;
}

bool mem_cgroup_oom_called(struct task_struct *task)
@@ -1298,7 +1237,6 @@ __mem_cgroup_uncharge_common(struct page
default:
break;
}
-
res_counter_uncharge(&mem->res, PAGE_SIZE);
if (do_swap_account && (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
res_counter_uncharge(&mem->memsw, PAGE_SIZE);
@@ -2148,6 +2086,8 @@ static void __mem_cgroup_free(struct mem
{
int node;

+ free_css_id(&mem_cgroup_subsys, &mem->css);
+
for_each_node_state(node, N_POSSIBLE)
free_mem_cgroup_per_zone_info(mem, node);

@@ -2185,11 +2125,12 @@ static struct cgroup_subsys_state *
mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
{
struct mem_cgroup *mem, *parent;
+ long error = -ENOMEM;
int node;

mem = mem_cgroup_alloc();
if (!mem)
- return ERR_PTR(-ENOMEM);
+ return ERR_PTR(error);

for_each_node_state(node, N_POSSIBLE)
if (alloc_mem_cgroup_per_zone_info(mem, node))
@@ -2210,7 +2151,8 @@ mem_cgroup_create(struct cgroup_subsys *
res_counter_init(&mem->res, NULL);
res_counter_init(&mem->memsw, NULL);
}
- mem->last_scanned_child = NULL;
+ mem->last_scanned_child = 0;
+ mem->scan_age = 0;
spin_lock_init(&mem->reclaim_param_lock);

if (parent)
@@ -2219,7 +2161,7 @@ mem_cgroup_create(struct cgroup_subsys *
return &mem->css;
free_out:
__mem_cgroup_free(mem);
- return ERR_PTR(-ENOMEM);
+ return ERR_PTR(error);
}

static void mem_cgroup_pre_destroy(struct cgroup_subsys *ss,
@@ -2270,6 +2212,7 @@ struct cgroup_subsys mem_cgroup_subsys =
.populate = mem_cgroup_populate,
.attach = mem_cgroup_move_task,
.early_init = 0,
+ .use_id = 1,
};

#ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP


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